FAL with stopping power or FMJ is one-shot-kill for a head shot, two shot kill anywhere else. If you use a holographic sight, its minimum damage increases as well, which guarantees a two shot kill from long range. Best AR in the game if you're quick enough with your digits.
I like the M16 as well, but I find you can control your ammo expenditure better with the FAL.
OMA is used for more things then just tubing. I use it on LMG's for a faster reload for example and it's also useful for getting my 2 claymores set up as fast as possible without having to wait for someone to die to get the blue bag they drop.
I also use it on the M21 EBR so I can just spam loads of bullets as fast as possible without having to worry about running out of ammo.
YOU PEOPLE SICKEN ME.
Really, though, it's all about mixing it up. I'm glad other people find other perks useful because I never use them, and if nobody else did, it'd be a pretty boring game.
OMA is used for this and this alone NOOB tubing,everybody ive seen with OMA has a noob tube,or they switch class to noob tube then to a RPD spray and pray class.The bottom pic will show what OMA is currently used for
and the reason ive played this game twice in ages