Eh. I like Ultron being Hank's creation because I think Tony already has enough going for him, while Hank doesn't.
I think the AoU film would have been better if, instead of it being a normal Hydra base they raid, it could be an old Pym facility that Hydra has set up shop in. Inside, Tony discovers the deactivated Ultron and decides to take him back for study and accidentally awakens him. That way he's still Pym's creation and Tony can be blamed for awakening him.