To answer the actual question. the best FLOW would always be a K&N. Nothing out flows it. However for Off-Road dusty conditions, even K&N recommends you get a Pre-Filter. They have two styles now. One is a foam-like material and the other is more of a cloth-like cover.
If FILTRATION is your priority, then nothing is better than a PAPER (or possibly stock) air filter. However you do sacrafice on the air intake.
Some outside test have shown that FOAM (ie Amsoil) and COTTON (ie K&N) both allow about the same amount of dirt in so if you are willing to sacrafice some filtration for flow, then Foam or Cotton is a toss up.