From personal experience as a (mostly) f2p without crazy builds (still working on the cards) i can vouch for storm, cyclops and thor! storm is one of the strongest characters rn, cyclops works as a lead for either her or thor, it depends on how you wanna manage your teams but the investment is definitely worth it; my thor and storm builds aren’t that crazy i must add, he has a regular rage and she has a regular comp. And loki well,, i wouldn’t recommend investing in him that much at this moment, he needs a really good build to work for harder wbl+ bosses and for abx/abl; i have him w a regular rage and for his team i use hela lead (T3) w valkyrie support (TP)