I used the m16 after my RPD ran out of bullets for my 22 kill spree on crossfire, it got me a fair few kills.
Then on my second 22 kill spree of the night my RPD ran out of bullets on ambush I picked up an m16 again, its a great gun but I didn't appriciate it when I first started online multiplayer. Unfortunetly i doesn't work at spraying oppoents when your surrounded by opponents, its not bad one on one, but when there are a number of people in front of you its not as effective as the RPD. That of course doesn't change the fact its solid at alomost any range, including close up. I especially love the iron sights of the m16, it sits perfectly still as you fire off a burst. I would say its better than the G3, which makes it a very immpresive gun. The G3 has better iron sights though.
If your aim isn't brilliant yet, the Saw will compensate for it by putting bullet holes in every concivable area of the map, making this perfect at firing at partially conceild targets that you normally wouldn't be confident of hitting. I used the SAW very effectively early on, I have changed to the RPD now because of the immense damage and ability to penetrate walls to kill people behind cover. But make no mistake you can rack up the kills with the saw, just make sure watch how many rounds you get through as the saw fires very quickly, the 100 rounds per clip goes much quicker than you would expect.