I have Hel, Gm, And Kaliden. Who would you like to see with these 3?
On defence, or?
20 pile of bacon
Offense…or is that a better defensive team?
All three of them are good heroes for both defense and offense imo…
Also hard to say who’d they pair with if you don’t tell us who you have lol 
If your bench allows, then on offence you could consider stacking against the strong heroes in the defence team you target, and pick heroes based on what specials the target team has. It means your attack team would be different based on who you attack.
For example if you attack a team with Boril tank, them a dispeller like Caedmon, Melendor or Sonya are very useful. Having both Caed and Mel in the attack team would also make your green tiles hit hard (stacking). On the other hand if you attack a team with Boldtusk tank, then Kiril, Grimm, Magni are a good team. GM tank - 3 blues, but helps with a cleanser like Rigard.
If you have one rainbow team, then take your strongest heroes. Hel, GM, Kadilen - could use a debuffer here (Grimm, Tiburtus, Gormek or Wilbur) and maybe a healer.