Your list and my list have some similarities; for me it depends on my level of expectations versus actual performance. For that reason I cannot put the Michigan State loss up there as a "disappointing" loss; while it would have been beyond fantastic to make a Final Four, we played up to our #2 seed, and most people came to regard that game as being the true national championship when it was all said and done.
For me;
#5) UCLA in '97 (had a 16-point second half lead at one point)
#4) Purdue in '17 (that team had such potential, even though Purdue was the slightly higher seed. I cried like a baby after that game, and I was 42 at the time)
#3) UCONN in '14 (Yes, UCONN went on to win it all, and Georges was injured. But, we were the higher seed and had beaten a very talented UNC team without Georges, which looking back on it is one of my all-time favorite wins. But, UCONN really controlled that game from start to finish, and I remember us just not playing very well at all.
#2) UAB in '15 (Enough said. I couldn't watch any more basketball for the rest of that day)
#1) F*ckin' Hampton in '01 (Honest to God, for at least a few years after that game, I couldn't physiologically watch the "One Shining Moment" montage when they showed the Hampton coach being carried around the court. My body would physically shake in anguish, true story).
My disappointment over these losses is a function of four things...
(1.) How big of a choke job was this individual game? Giving up the huge lead against UCLA, the decent lead against Michigan State, and the last few possessions against Hampton and Aaron Craft count.
(2.) How far under expectations (loosely defined by their seeds, but not entirely) did the team perform? The big upsets... Hampton, UAB... are the ones that linger in my mind here. Those teams should have done so much more. I feel the same way about talented, experienced, and senior-heavy teams that probably could have played better than their seeds, the primary examples of these being Georges' and then Monté's senior years.
(3.) What would it have accomplished had we won. Sure, #1 Michigan State was a great team and losing to them in the Elite Eight as a #2 is playing up to our seed. But if we won that game, we're in the Final Four, and our opponents would have been #8 Wisconsin (8-8 in the Big Ten) and then #5 Florida (12-4 in the SEC). I would not
guarantee a national championship under those circumstances, but we would have been
heavily favored in both games.
So the path to a Natty was wide open if we could have gotten past Michigan State. We just didn't. That is always going to be the most disappointing loss in program history until another opportunity like that presents itself. Michigan State took care of both of them pretty easily. I would imagine we would have, too, but alas.
(4.) Just how likeable the team was. The 2019 team was not all that likeable, and the 2017 team was.
Based on those criteria, I would probably say...
#5 1997 against UCLA
#4 2001 against Hampton
#3 2016 against UAB
#2 2017 against Purdue
#1 2000 against Michigan State