What are the best guns in combat arms? Well, it depends on what map your playing really. If you like to play on small maps like junk flea, then I recommend using the UMP. The UMP is very powerful as it shoots a .45 caliber round at a decent rate. On small maps, this gun can dominate.
On the other hand, you have your big maps. These maps favor better for rifle users. One of the best all around GP rifles is the G36 because it has a built in scope and does a very high amount of damage. It is also very effective at close range.