Well we got to see peak T-Mac. He was incredible at that peak. If you're talking about the healthy versions we saw, this isn't really a competition.
If we're talking about potential, well I'm torn. I was a huge Penny fan and thought he was going to be an all-time great when he was young. But he also fell the furthest off the cliff of the 3 and his numbers had already come way down when Shaq left, even before the injuries (though obviously a small sample since the injuries started shortly after). And Grant Hill is the most efficient of the bunch and by far the best defender of the bunch, so it's tempting to take him as well. But at the end of the day, I'm taking the known quantity in T-Mac anyways.