I've been using AoP since I got him early in the game, and he's been a great asset to my team. I've been primarily focusing my skill shards on my Eddies, but I decided to look at allies, since some of the Champions I've been using are pretty powerful after skill upgrades.
I'm looking at AoP's Storm skill, because it's an AoE that will have an added 70% damage when maxed, as well as an increase to 70% chance of shock. I know people praise the blue Allied Soldier for skill upgrades, as his base attack is an AoE, upgrades to 55%, and is low cost in skill shards. It'll take many more skill shards to upgrade AoP, taking into consideration that he has a base skill that'll steal them along the way. The end result would be more powerful than Allied Soldier though, so I'm feeling it would be worth the investment.
I wanted to get some more opinions on it though before proceeding.