Churchill - swap for Maus (as mentioned if you want to use her in the future, it's better to keep her in your team);
KV-2 - swap with T-34 for defense-type medium or Easy 8/Chi-Ri for offense;
Semo - high penetration skill good vs heavies, but can be swapped with Chi-ri or Hellcat for more DPS;
Firefly - swap with AC4 (same skill but has better stats and 15% base evasion);
main heavy - Tiger sisters or Maus; support heavy - IS;
defense medium - T34; offense medium - Chi-ri, Easy 8; AC4 - anti-evasion; M26 - versatile medium;
Hetzer - fast TD with 7 sec stun skill; Jagd - solid TD, still using her myself; Elefant - ok base penetration + crit shot skill, good vs heavies or evasion tanks; Hellcat - glass cannon;
M24 - good buff/debuff;
Stuart / Sherman Croc- assassin tanks, should clear invasions fast.