I have the MOE on my M&P 15. Great handguard, not free floated, but an all around good bargain.
All I have mounted on it right now is a sling mount, but will soon mount a flashlight.
If you want the best one IMO, go with Troy. Might be out of your price range, but just throwing it out there.
http://store.troyind.com/Drop_In_BattleRails_s/4.htm