7 STAR AG

P2099 or Jack. P2099 gets a lot of benefit just from sig 1, and it moves him from a solid champ to a quite good one. Jack is - well Jack.

Ultron needs alot of sigs before it is really worth it, so you should only do that if you REALLY like him and have a bunch of sigs to invest in him.

AOLOG

Guardian or Prowler. I know you don't have them yet but when you do, you will wish you saved it.

The_Doctor_24_1

I'd take Ultron easily. The sigs will come little by little, but by rarity he's the obvious choice. I'd never take someone who's on the basic because it may become your next pull and believe me, that feeling you get by pulling the champ you just used an AG on it's horrible and the 7* AG are super rare at the moment