No particular class has any advantage with any particular weapon type (the lore speaks otherwise of course). A better question to ask would be "what are the best rifles and guns available from level 26?". (which I don't really have an answer for any way XD )
That said, there is the exotic scout rifle Tlaloc and a fusion rifle whose name I can't remember for the life of me, that can only be equipped by a warlock.
It doesn't really matter, it only matters to what play style you choose. If you're an aggressive player, you usually would want to use weapons that cater to more short and medium range engagements (The Last Word /MIDA Multi-Tool and META weapons and a Shotgun combo would be preferable). If you like to take your time with your shots, I recommend going with weapons that cater to medium and long range engagements (META weapons (high RoF Pulse Rifles and High Impact Scout Rifles)/MIDA-Multi Tool and a Sniper Rifle would be preferable). If you want to get kills from all ranges, I recommend a balanced role (Any Meta weapon and a Special that its range is the opposite to what you're using as Primary is preferable). It matters to what play style you choose. To Silicon Soldier: I think it's Susanoo .