A very interesting question, and for the time being I also would probably have to vote for Larry, as he seemed to hold himself the best in solo performances like GYPPED IN THE PENTHOUSE, HE COOKED HIS GOOSE, and even CUCKOO ON A CHOO-CHOO (I don’t like the short as a whole, but his performance is pretty impressive).
I think Moe was so closely identified with his personality that it would have been hard to see him as anything but a supporting player, usually as the villain.
As for Curly, his high-pitched voice would have made him a natural for cartoon work, usually playing little characters like fleas or other insects. Had the Fleischer Studios not been located in Florida at the time, I feel he would have been the perfect choice for the voice of “Swat the Fly” in MR. BUG GOES TO TOWN.