Wasp is far, far better than Kingpin. I do enjoy Kingpin's yellow power as amusingly inspired by the comics, but it takes forever to get going.She-Hulk... well, she has a lot of health, and her red power will often destroy hard-to-match enemy tiles at the bottom of the board. I will occasionally call her up while somebody on my A-team is benched and healing. She works well with Dr Strange because she'll be the one to match blue and stay in front.If you've got a yellow Okoye, note that she's practically unkillable with that power, especially as it *restores* health, and not just heals for the duration of the match. I really enjoyed using Okoye as my tank, Strange in the rear, and alternating between the two Wasps and Kraven as my "running backs" in the recent Unstable Iso-8 event.
I'm pretty much done with recruiting 3* characters, as the few I don't have are ones I don't want at all (Storm, Capt. Marvel, Daken, Gambit, and She-Hulk...unless someone can make a really good case for She-Hulk).
Wasp! Team her yellow power with 3* Falcon - fire his purple, flip those shields and then absolutely shred the enemy.
You're too early in the game for 5*s, but that Okoye Black might be the only exception. I'd hold on to that one like it's gold.
I'll take Coulson every day over Kingpin if I want somebody doing countdown spam on yellow because his passives are excellent. It is actually kind of fun to run both those characters together even though they overlap, because Kingpin's CDs seem to do way more damage, and Coulson can shorten them up by matching team up tiles away.