In general, the more expensive the shorts, the longer the distance you can expect them to be comfortable. I wouldn't bother with the super-cheap shorts. I really like the Sugoi Evolution shorts (though mine are the old version) and Primal Wear's Prima shorts. I also have a pair of Castelli shorts, and while I like the fabric, I don't particularly like the chamois. I just ordered a few pairs of Pearl Izumi shorts. Let's see how they behave.