If I'm using piped Norvels, I go with a Master Airscrew 9 x4. An APC 8x5 screams big time, but I usually need more than a 6 oz tank for a 5 minute round.

Without pipes, I like APC 8x5's on Norvels.

OS FX 25's seem to like Master Airscrew 9x4's, even unpiped they scream and hold speed.

APC's are probably better props, but I break them too often in the air and like the durability of Master Airscrew. I hate not finishing a round because I hit someone with my prop, and break it.