MN227,
The thing is, M7 & M9 won't normally fit on a 16" (you already know this) so it is really dependent on the extension. All the bayonet lugs I have seen first hand are all the same, and I stick with flash hiders that are mil-spec in outside dimension. I think that leaves F/H like Colt, Gem-Tech, AAC, KAC, Vortex, and maybe Phantom? Probably others too. I bought one of those M7 Bayonets from PreBanArms/Cuzco for 16" carbines, and it is really nice. The bayonet is a real Colt and the extension is made very well and finished perfectly - it all looks like factory.
The standard for bayonets, flash hiders, and bayonet mounts is a matter of mil-spec dimensions. Except for those barrels with a funky flash hider or muzzle brake, I don't think you will have a problem.
P.S. I also have an M7 bayonet that fits the original Bushmaster 5.5" flash hider (mounted on a 11.5" barrel). I don't know where you get those cause the flash hider is larger than a standard F/H I think.