I've found the best guns to use for me are the Hydra Shotgun and the unlimited rocket launcher. If you don't have the unlimited Rocket Launcher I'd use the Hydra, PSG1 and Mag500. If you do have the unlimited Rocket Launcher don't rely to much on it as rushing enemies will make you blow yourself up and sometimes your AI partner runs in front of you and the partner will cause both of you to be blown up.
The Mag500 is amazingly powerful but not fast enough for Professional, if you get rushed your dead with the mag on pro. Use it for the big guys and bosses, use the Hydra for hordes of majini.
This is of course assuming you even have these guns and unlimited ammo for them. If you don't you can get the best money/bonus points combo from running 1-2. 10 minutes to make 2k points and 12k gold on Veteran.