(Just comparing their BYU days)
Cosic- A BYU legend. A 6' 11" center that could dribble and pass the ball like Pete Maravich. He also had a huge wing span and was a shot blocker. Great on defense. I know how entertaining Ainge and Jimmer were, but in my book Cosic was the most entertaining. Easily the best BYU Center/5 in BYU's history. It is a great compliment to him that Walton thinks he's BYU's greatest.
Ainge
Absolute tenacious BYU player. Terrific on the defensive side as well as the offense. PPG would have significantly increased had the three point existed in those days. Don't forget that BYU basketball in the mid seventies was struggling. Some of those teams just weren't very good. Everything changed when Ainge arrived.
Jimmer
Probably the most high profile athlete in BYU's history. Had the best range of any BYU player on the court. Best offensive player BYU has ever had. He very rarely lost his cool when playing. (if ever) Always played under control, but was still intense.
My BYU basketball all time MVP? It's a tough call, but I'd flip a coin between Ainge and Fredette. Either would be very worthy to be called BYU's best ever. Guess I'd give them co equal MVP's with honorable mention to Cosic.