You can never go wrong with the M416. I find its among the best guns in the game because it has little recoil. Downside is it doesn't pack much power, but the low recoil makes up for that.
I'm using the M416 on PC because I use a PS3 controller and I'm not used to it. Feel the joysticks are too sensitive and therefor my aim can be a little off so I prefer the low recoil to make up for any missed shots. Where as with the AEK or A91 on Xbox I need to be more on point to make it rain.