Because so many of these sound dope as fukk, I figure you gotta break it down to get to one singular answer. So I’ll look at it through this scope:
Triple threat matches are still a fairly modern concept, so you’d have to figure a lot of the older names on that list might not do so well with adapting to one because they never had to work it. Flair/Savage/Steamboat sounds tantalizing, but Savage intricately planned his matches out in advance, how does that fare to a triple threat setting?
Plus some guys have chemistry with each other while others don’t. Hoegan/Savage had chemistry, Flair/Hoegan not so much.
Saying all that, I’d go with Rock/HHH/Austin. All three guys had chemistry with each other after years of working together and they all could work triple threats. Plus since it takes place in 2001, that was HHH’s peak in ring before the quad injuries, Austin’s last good year before he hung it up, and Rock as he slowly left for Hollywood. Literally all 3 dudes at their peaks as workers and arguably characters.