Lang Lang, Pletnev, Andsnes, Fiorentino, Ashkenazy, Hough all seem very pleasant and well-adjusted people. Godowsky and Schnabel were both famous for their sense of humor. Gould was a total nut, but I'd be fascinated to meet him.
I've heard things suggesting Barenboim is a sleazy character as well. Gieseking and Cortot were both Nazi sympathizers.
Greats like Ricther, Horowitz, Rubinstein always strike me as the kind of egotistical pianists I admire but would not particularly want to have tea with. Too overpowering.