There were a few changes from the Battlefield Hardline Beta to the full release which means that the best gun in Battlefield Hardline also has changed. The best gun in the Battlefield Hardline Beta was the M416 which still remains highly competitive. The AKM is also very good.
The Best Gun in Battlefield Hardline
At this point, future patches pending, the best guns in Battlefield Hardline are the K10 and the SCAR-H. The K10 shoots very quickly and is devastating at close range. The SCAR-H hits like a truck and is best at medium and long range, although it does have a small magazine size.