I'd agree, though this is a very tough call and an excellent question as they all have similar credentials. Stick was definitely the smoothest of the lot and had no real weaknesses. When he was on, like in the Wimbledon final against Becker, he seemed unbeatable.
That said, I think Ivanisevic and Krajicek had better serves. Stick's was still great, obviously, but I'd say Ivanisevic and Krajicek may be in the top 5 servers of all time. Stick is a bit outside of that.
Krajicek may have been a tad better at the net, but it's hard to say. Ivanisevic volleyed just okay. Krajicek's return wasn't too great, nor was his backhand.
So I see the other two as having more semi-weaknesses. Of course, this doesn't take the mental game into account.
The real shame is that we lost all these players too soon, especially Stick and Krajicek. Thought I'd see Stick battling Sampras for many majors, but it never happened. Damn injuries!!