Who should I take to r4

Killercamine

6 star Doctor doom or cosmic ghost rider awakened.

Also I have 2k units left should I go for bundle 1 or bundle 3?

DigletGaming

I'd say that you rank 4, Doctor Doom. GCR is probably the way to go if you're trying to do battlegrounds, longer content (AOL, LOL, etc.), or EOP.