First, do what everybody should do and complete the two month hire gun pilgrimage.
By then you should have figured out how you like to play, and what kind of gun you suit, whether it's a light gun, a heavy gun, a gas gun, an electric gun, a machine gun, a dmr or anywhere in between.
I personally like having a light gun as my rig is heavy enough, and I most enjoy close quarters indoor fighting, rather than outdoor full-auto fest spraying, where I usually grab my AEG and it's the only time I would consider using a high-cap.
On the other hand, my mate loves having one gun and a high cap, leading a charge whilst laying down some crazy suppressing fire, he wears little gear on him and so can run at the enemy all day.
Were all different. And you probably don't play like each of us because you have your own style