i use the MP7 Ext. (SMG)
Its a very good weapon with a EOTech Scope.
and the PSG1 (sniper)
This is what i use and i think these are the best weapons for now.
If you are willing to buy cash weapons buy them, because they obviously better than credit guns.
I myself use UMP45 Ext. , PSG-1 and I might buy myself another one of the new guns later on. I was thinking G36C Ext.
For a starter like yourself I would suggest a low recoil weapon. So go for SG550 if you like a good overall gun, go for M4A1 if you can handle more recoil or try the F200 if you like tap-firing/burst firing.
Welcome to Project Blackout (: