Rank up Warlock or Ultron?

Biscuits2015

I have enough Catalysts to EITHER upgrade my best Champion 5* Warlock to Rank 5 OR my second best Champion 5* Ultron to Rank 4.

Which is the better option?

Rank 5 Warlock and Rank 3 Ultron

OR

Rank 4 Warlock and Rank 4 Ultron?

Colonaut123

Warlock, no doubt.

Hollowborn

R5 Warlock

Ethereality

Warlock and it's not even a contest.

mattress

Warlock