Who should I R4?

Apyr_droog

I've got enough materials for 2 new R4's, but I don't know who to choose. Please tell me who you'd R4!

All champions are or can be awakened, but low sig. Except Valkrie and Tigra and I could get tech champs to sig 100 at least.

My current R4's are:
Knull
Nick Fury
Galan
Kitty Pryde
Scorpion