I love, and have had most success with, the humble 'Godwyn-Deaz' Pattern .998 caliber Boltgun. I don't like using Kraken bolts, the red massive shells look tacky, and get you seen. I use the targeter perk and aim for the chest/head area, middle to long range, it's deadly, accurate, and most people leave you alone because you're a humble Bolter wielding brother... (That sounds like a bad exploitation movie set in the 41st Millenium now, doesn't it?
)
One other reason I love that set up is the challenge of dealing with assault marines, it's really satisfying to pick off the jump packers with superior positioning and mass-reactive bolt shells.
While I currently have a love affair with the stalker, the bolter still has my hearts.
Kraken/targeter ftw. Every now and again when I feel the need to dispense death like a true son of Khan, there's nothing else I would choose.
The Emperor Protects, but having a loaded Botler can't hurt either....
Also, the Storm Bolter, no perks, deadly. Feather that trigger right, and I can snipe cross map with silly effect!
Kumbaya... MOTHERFUCKER.