ASE Ultra (AU-S5) and the MAE T12 (full length) are the two best I've used - for me they met the needs of being light, not adding too much length, and very good noise reduction.
I currently used the MAE because I prefer the balance it gives and it barely potrudes past the barrel. I also found accuracy was improved due to lack of muzzle flip, however as a rule adding weight to your rifle barrel can make it do funny things when it's hot - and over barrel mods do hold the heat against the barrel. They are only really meant as hunting moderators as they get very hot with continuous fire and mark the barrel.