You really dont need strong weapons actually because your free weapon UMP is better than most weapons.
If you know how to play UMP is your best friend. Ump's headshot damage is 21 and has less recoil.
So UMP better than; (According to my play style and experience in game)
GA3A
BlastGun
Vector X
G36
Mini-gun
All you need to do is cover your range and try to do headshoots calmly.