I'm not a promoter (to care about what is the biggest crowd draw)
or a MMA expert (so I'll refrain from expressing my opinion on MMA matchups)
Instead I'll tackle this on the principle of the most balanced (in my opinion) fight.
So I voted Tyson Vs Hoost (two legends, same age group, comparable experience, stamina - or lack of
clear advantages on different areas (box vs kick) but also no marked deficiencies for any fighter, provided Tyson takes at least a 3 month intensive kick handling preparation)
Also both would hate to to out a loser and would probably give it their all (as representatives of two worlds)
Other K-1 option not viable in my opinion for different reasons (unless someone of course thinks to "prove" a point by making an intentional mismatched fight):
Sapp = I won't even go into that again, it would be a farce (and he will most probably need serious medical attention)
Abidi = Also not open to serious debate, his hand tecnique, defense is terrible and the mentality is all wrong (he'll be KO'd for sure)
Cro-Cop = one of the fighters I like, complete standup fighter, but he does tend to get intimidated if he takes a couple of good blows (and he WILL get hit if he faces Tyson). Also I don't like the idea of piting a fighter in his prime against a fighter who's on the way out (what would it prove either way?)
Bonjasky = maybe in 2 years (but by that time Tyson will most probably be even more downhill). Let's face it, Bonjasky has been lucky (maybe pampered?) so far. He's the up and coming "big star" and he's being protected by promoters (saved for later), building his reputation against inferior opponents. After I've seen him fight against Ignasov/Cro-Cop/Hoost/Aerts or any of the heavyweights from New Zealand maybe I'll think differently, but if he fights an even moderately prepared Tyson NOW, he's in for more than he can handle (they wouldn't let him risk the pretty face anyway
)
Hoost = my choice for reasons above (end/beginning or era type of fight)