Forgive me if this is too simplistic an answer, but buy whichever one fits your hand the best. An uncomfortable mouse sucks no matter what the price or warranty is like. And if you do any gaming, make sure you buy one of the higher-end products. The cheapo optical mice (even from Microsoft and Logitech) only scan movement about a quarter as often as the better ones, so the mouse will spazz-out on really quick moves.