I'd give Mike the slight edge here - his attitude is much more relaxed compared to his fighting days. What he lacks in fire, I think he makes up for in maturity (of course that may just be the meds and the pot at work, but I'll give him the benefit of the doubt). Holyfield will always have that warrior's mental fortitude, but I think Mike almost beat himself when they fought by being too wound up and unable to fact adversity. I think he's more settled now, a bit less intense - how well that translates into his ability to fight, who knows, but a more relaxed fighter (old Foreman) tends to be more effective. Evander probably has an edge in conditioning, having spent less time out of the ring compared to Mike - but he's also been in many more wars going back to his CW days. His body (and skull) have taken a lot of punishment. I worry more about his well-being than Tyson. If they do get together, hopefully it's just a four or six round exhibition for charity or whatever - though both could apparently use the dough.
And now James Toney wants in on the fights /exhibition s lol. Suppose there's a revenge factor in there for Holyfield.