The epic heroes are very well-balanced (unlike the legendaries). There are very few duds among the fours and most are capable of playing a role to play in a balanced team.
That said, there are some in each color who stand out on a defense: Boldtusk, Wilbur, and Colen; Kiril, Grimm, and Triton; Buddy and Hansel; Rigard and Li Xiu.
I think today I’d go with Triton-Boldtusk-Li Xiu-Buddy-Rigard as the best epic defensive team.
Defense:
Rigard - Caedmon - Colen - Peters - Kiril
Offense: too many combinations that can be made so no recommendations
I should say, it’s been looong time since I raided with and against nothing but fours. When I did I remember hating teams with two healers—but maybe that was because I didn’t have many to attack with.
If I was running just one healer, I’d go Triton-Rigard-Li Xiu-Buddy-Colen.
If not going with a rainbow, I’d say tank Buddy and surround him with Triton and Kiril, with Boldtusk and Colen on the wings.
Sounds good. With the minions and all. 
Keshhrek is hard core for a 4*…Rigard also a heavy
I’d like to submit my own, for best 4* raid offense team
Sabina - Gormek - Cyprian - Colen - Boldtusk
2668 cups
Defense… no 4* defense will keep you in diamond