Banner(s)
The thing with Tony, is that he's too smart, but we're still smarter and he knows that. If he cuts you out of plans, if he's cagey or doing things behind your back, he's either doing something he thinks is in your best interest (See: Hulkbuster suit) or he's doing something he knows you'll tell him is stupid, either way, the last thing you want to do is let him get away with it.
Yeah, yes. Building a Hulkbuster suit was a good idea, sure. You don't have to stop him. Just make sure you know what he's doing and can stop him if you have to.
Because seriously, Banner. You knew Ultron was a bad idea, you must have.