Sniper rifles.

Most ranges offer up to 175 XP per kill with headshots, and chaining them would result in XP increases due to getting multi kills.

DMRs and Sniper Rifle. 

I'll say that depends, you gotta experiment with different guns before you find the best . Some may find snipers the best because your chances of dying are low (unless the other team has a good sniper or a flanker). Personally for me, it's assault rifles and PDWs, they are great for CQB and handy if you know the map well, allowing you to cut off enemies. But I think that using silenced weapons (intergrated or not) can be helpful while grinding

necropost alert reeeeeeeee

also RPK is good for grinding imo

• Honey Badger with stubby and green laser only

Its good on metro with stubby and green laser

• Scar Hamr

• Rpk74 and MG3KWS

• Some snipers or DMRS

• PPSH-41

Many more.