Whom to upgrade guys?

Macha1275

This is my six star roster. Next is 6.3. Going for TB. Whom should I upgrade next?

willrun4adonut

Sinister, Doom, Serpent in that order imo.

BuggyDClown

Herc, Doom, Sinister, Hulkling, BRB, AA,

TBH your entire have almost all great champs which will be useful till act 8 as well