Rank em.

BATMAN1

Ok guys I have a fun game. Let’s rank sets in order from best to worst. Every symbol counts as its own set not including holiday set and the duel battle card set. 

Ok best set in the game I’m going with EM. 

Worst set maybe oath of the gate watch although there are some very cool cards in there.

sorry too tired to do the whole list. 

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Theros

Best is DOM. All cards in that set are good and usable.
 other sets octagon has made are horrendously unplayable  except for a few outliers some of which look meta wrapping.
2nd best has to be SOI

The worst is RNA. Adapt mechanic is weak. Even energy many regard as lacking is better than adapt for few reasons:
Energy creates more energy gems when the same creature is played multiple time or teferi blinked. If I play 2 creatures with energy 2 I get 4 energy gems. On the other hand, playing multiple or blinked copies of an adapt creature does not create additional adapt gems. This is the no 1 limitin factor. All other mechanics in game like void, treasures.. do not act like adapt.

Tremayne

Theros said:

Best is DOM. All cards in that set are good and usable.
 other sets octagon has made are horrendously unplayable  except for a few outliers some of which look meta wrapping.
2nd best has to be SOI

The worst is RNA. Adapt mechanic is weak. Even energy many regard as lacking is better than adapt for few reasons:
Energy creates more energy gems when the same creature is played multiple time or teferi blinked. If I play 2 creatures with energy 2 I get 4 energy gems. On the other hand, playing multiple or blinked copies of an adapt creature does not create additional adapt gems. This is the no 1 limitin factor. All other mechanics in game like void, treasures.. do not act like adapt.

@Theros  - There is another difference between adapt and energize (and every other mechanism) whenever your opponent triggers adapt gems, they are returned to the battlefield. That is not something energised does.

Does that constitute sufficient compensation to you?

wereotter

Going from a different point of view.... my opinion is that the worst set is a tossup between SOI and EMN. Granted both sets are extremely powerful, but it's exactly that ridiculous power level that broke the game for a long time and was one of the main reasons Standard had to be introduced. Newer sets couldn't compete with them, and cards, in general, needed to be powered down to match.

Best set, in my opinion, is probably Guilds of Ravnica. There are some powerful bombs in the set to be sure, but also the mechanics make sense and are well implemented. Many of the mythic rare cards serve to either support or benefit from the mechanics of the various guilds, and the way the guilds mechanics are set up work well with other guilds that share a color Surveil can put cards in the graveyard for jump start and undergrowth, convoke works well with both the boros and golgari methods of putting out lots of tokens, and other good synergies can be found. The only shame with this set is there weren't many events to use these cards in.

stikxs

DOM was a very good set. It's all-around decently strong, though that is kind of relative to accompanying sets. Its other high point is it is pretty smooth on power levels/rarity. None of the cards are instant wins (except maybe Naru with other things), and while it has big threats they can also be countered, but also it has some C/UC value powerhouses.

I'm not too familiar with sets before AKH, but I know there are some serious power-offenders there. I don't think any sets have really been bad on the whole, but there have definitely continued to be over-tuned cards coming out. StV is so powerful you use it still on non-blue PW that have red access. If you have blue, you use BSZ. It used to be green with season's past, rishkar's, and HoP, but instead of evening the playing field they just moved the power to blue.

I think RNA is as much a victim of other sets as it is a weak set. Yes, it feels weaker compared to the rest of standard and some of the mechanics are lacking (adapt). But if the plan is to tone down power levels to make things less spikey it's going to have to start somewhere. If future sets stay inline with GRN/RNA then I think RNA won't be as lacking when the next big standard rotation happens (unfortunately for RNA it will be old news by then). Given that RNA isn't received as well as previous sets it wouldn't surprise me if sales sag a bit, which is also a recipe for management to push power cards again that will make money and push back to that cycle of OP things.

Gilesclone

By far the worst set is M19.  It has BSZ but very little else and card by card it’s just awful.  By rarity, Its best cards by rarity in common and uncommon are worse than the average of PQ commons and uncommons.  Probably rare and mythic too, but I haven’t had time to confirm that.

Best is harder.  Maybe Dom or Amonkhet?  BfZ, SoI, and Kaladesh all had incredibly powerful cards at the top but real garbage below.  I’d probably go with Dom.  It was just solid all around without anything really broken.

IM_CARLOS

Akh was meta warping with cycling, so I vote akh for best. 

Laeuftbeidir

Best set : DOM. It has the most balanced power over the colors and rarities I'd say. Also very interesting combos.

Worst set : that's hard. M19 gave us BSZ. The ravnica sets dont have relevant events, so they feel pointless.. But then there was cycling.. AKH it is. The worst set so far.

Tilwin90

I actually find the current blend of sets to be really interesting as they all bring a different approach to things. However, leaving overpowered cards aside, here is my ranking:

1) GRN - While we see serious color breaks in MTGPQ, let's keep in mind it is not paper magic. I actually like the diversity the dual colored cards bring. Unlike Ixalan triple colored threats, the diversity here is formidable and ironically gives immense power to mono colored walkers. Ever since GRN was released I started playing again with Koth, Elspeth, Vivien and Jace2.
Great fun masterpieces without any being necessarily overpowered without going very specific (Bloodbond March requires filling the graveyard, Glimpse also focuses on graveyard strategies, Bloodletter Quill is a great alternative to Alhammaret's Archive without being OP, Stitch in Time is powerful in specific decks but I blame its overpowered status on BSZ, Firemane Angel quite annoying to get rid of but tons of fun).
Set mechanics are rather meh.
We are lucky to have gotten Ral, as Vraska was a horrible walker.

2) RNA - Same reasons as above, though the Masterpieces look slightly less crazy and more downpowered. Probably will see more play post rotation. Other than that this set brought back a lot of flexible removal, especially in white. 
All three walkers are not worth my attention, though now if I had to choose between Domri and Samut I might be tempted to go with Domri (though now that Sarkhan3 is around I see little reason to get either).

3) DOM - I haven't had so much fun with any other mechanics as I did with Historic. Besides this, cards like Rupture Spire/Scapeshift, Jodah, Oath of Teferi and Primevals' Glorious Rebirth opened up some super fun builds. 
Even the tribal factor proved to be easier to build than in IXN. (read below) Definitely a great set that I enjoyed.
Masterpieces were super mehsterpieces here, yet somehow I didn't mind them in the context of the set.
Naru Meha was a mistake that lead to some very awkward "fixes", and it shows that some cards just shouldn't be transposed in MTGPQ.
It also brought some really fun and powerful walkers in the form of Teferi and Karn, with Jaya also being lots of fun.

4) M19 - I have only one word: Arcades. He quickly became my favorite card in both Standard and Legacy and I hate tons tons of fun with it.
I hated the land matters theme as in spite of trying to push it, without the guildgates it felt very meh (and even with the guildgates I dislike filling my deck with lots of vulnerable lands that otherwise don't do much).
I didn't mind some of the powerful masterpieces, though my dislike here is the separation in "the good and the bad masterpiece of the color". There is no denying that BSZ, Ball Lightning, Luminarch Ascension, Plague Wind and Summoner's Pact are vastly superior to Bident, Courser, Eidolon, Hell's Caretaker and even Decree of Justice. 
The walkers here were super meh save for Vivien which brought a very nice mono green addition to my collection.

5) RIX - Oh boy, a small set that came up after the hated XLN and kind of infused it with more power due to its tribal nature. It brought some fun cards to brew with (I'm looking here at Azor's Gateway, Azor himself, Ghalta, and naturally Zacama).
It's slightly higher than XLN due to actually enabling tribal strategies and infusing Standard with some powerful cards.
It brought some of the most bonkers cards that made matches super oppressive. I am looking here at Etali, Ghalta and Sphinx's Decree (a card that could potentially indefinitely shut down 8/10 cards of your opponent was plain stupid)
The masterpieces were definitely not memorable and probably the only elite packs I never bothered to chase. 
Walkers were also not half bad, with Huatli2 being a very nice upgrade of the parasitic Ajani2. 

6) XLN - The hated set that I ended up sort of liking. None of the mechanics were exciting for me.
Like Kaladesh, in order to enjoy the tribal value of the set you needed to get access to quite a few mythics to get the job done, and dinos proved to be the undeniably strongest tribe. This was all thanks to RIX though... prior RIX, tribals were rather meh and felt pushed down our throats due to events without being that much fun.
It enabled the most oppressive combo of that format in the form of Settle the Wreckage + Starfield of Nyx (alas, I rarely see it being played nowadays) and it was the reason why the white node in RTO was so dreaded by me at the time.
Masterpieces were incredibly polarizing here, with only a handful proving to be fun and valuable (Sanguine Bond and Blood Baron of Vizkopa falling into this category). Yes, Swords of Plowshares is powerful, and it's quite sad to see it end up more or less replaceable with a RNA common now (yes, I know exile and destroy are not the exact same thing). 
Walkers here were rather terrible and showed that Oktagon had a lot to learn in this direction (and they later did). I still haven't gotten Jace3 or Huatli1 and fail to see the reason to grab them. Vraska1 was interesting because of her unique and long-awaited color combination.

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