https://forums.d3go.com/discussion/56176/a-mostly-accurate-4-ranking-final-update-8-11-18/p1This hasn't been updated in about a year, but I'm not sure any of the 4-stars released since then would quality as "top tier." I'd say Domino is probably the best one that's not in this list thanks to her Black generation and board shake, but she's not Top 10.Edit - Looking at those rankings, I'd say that 4-star Rocket and Groot has moved up from #16 on the list thanks to some of the other characters that have been released...
I still say that Vulture is the best transitional 4*, since he is so versatile. Removes himself from taking harm to generate AP, does big AoE damage, can clear out specials, can be fed by strong 3s like Fist, can feed other characters at all tiers. His big drawback is that he's often the last man standing as a result of leaving your other 2 characters to eat a lot of damage while he's flying. Even with 2 5* champions on my roster, Occasionally in SCL9 I'll have to fall back on Vulture/G4mora to stun-lock the harder 5e nodes in some story missions on later clears.