Which is the best?
Smaller maps -> Boltshot.
Bigger maps -> Pistol.
Any map with a vehicle -> Plasma Pistol.
My opinion
its entirely situational, i personally run with the plasma pistol on any map that runs vehicles and vary between boltshot and pistol on small maps
Plasma Pistol, unless its a really small map. Then Boltshot.
Depends plasma pistol for vehicle maps and regular pistol for everything else.
Boltshot - excellent for close quarters as it provides a type of small shotgun
plasma pistol - anti vehicle and good to take down players shields
magnum - good for fast headshots of an enermy sheilds are down and can save your life when in danger