Ones with built-in warmers that grip on tarmac/dirt/snow would be best, but nobody makes them yet. We tried a few combinations of tires from Pirelli. For practice, I really liked an intermediate rain front and soft slick rear. Pressures were a little lower to try to keep heat in the tires (there was still snow on the ground). But before the race, we switched to a soft front slick because race-day temperature was much higher.