aks and armalites, seam to be the most popular, with any assault rifle and most smgs being a good choice. aim for a gun with 350 fps upper limit is 400 fps. avoid bolt actions and other sniper rifles like the plague.
tm and classic army, are good, so is g&p, and some china guns arn't bad for starters like a jg. arguably best aks are realsword and best ar would be a systema ptw