For me, these are the best epic heroes that I have:
Red: Boldtusk and costume (fully emblemed costumed version charges mana in 6 red tiles during rush wars and rush raid tourneys even without the support of a mana troop), Wilbur, Guardian Falcon, costumed Colen, Sumle and Shadereave.
Blue: Kiril and costume (fully emblemed costumed version charges mana in 6 blue tiles during rush wars and rush raid tourneys even without the support of a mana troop), Sapphire, Sonya and costume (fully emblemed costumed version charges mana in 6 blue tiles during rush wars and raid tourneys even without the support of a mana troop), Jott (red titan purpose), and Grimm w/ MCB.
Green: Almur, Brynhild, Caedmon and costume (fully emblemed original version w/ MCB charges mana in 6 green tiles during rush wars and rush raid tourneys even without the support of a mana troop), Melandor and costume (fully emblemed original version w/ MCB charges mana in 6 green tiles during rush wars and rush raid tourneys even without the support of a mana troop), Skittleskull and costume (fully emblemed original version w/ MCB charges mana in 6 green tiles during rush wars and rush raid tourneys even without the support of a mana troop), Buddy, Marcel, and Jack O’Hare.
Yellow: Wu Kong w/ MCB (for general purpose titan and mythic titans, also on most challenge events), Li Xiu w/ MCB (fully emblemed original version w/ MCB charges mana in 6 yellow tiles during rush wars and rush raid tourneys even without the support of a mana troop), Guardian Jackal, Lady Woolerton, Gullinbursti, Mist, Gretel and maybe costumed Chao (if fully emblemed since he can speed up mana generation even w/o a mana troop on certain conditions).
Dark: Rigard and costume, Sabina and costume, Tiburtus and costume, Proteus, and Ametrine.
There are still others that are very good. I just don’t have them.