If you specifically want a normal damage gun because you only want to carry one gun and don't want it to have damage type weaknesses, probably Valiance will suit you better. Besides the flexibility in movement, it has much longer range than the pepperbox line, and isn't that what you're wanting a gun for in the first place? Iron Slug might also fit the bill, here. I understand it's easier to hit dodging monsters with, but it's a 2-shot gun that roots you while you fire. Being rooted can definitely be a disadvantage, such as when you need to weave between volleys from gun puppies while you shoot.

To be honest if you're going to go through the trouble of leveling up the magnus line Callahan is really what you should be getting. Valiance will most likely have the best DPS unless you are using your pepperbox as a shotgun and going point-blank (this is where you'd really rather have a sword). Standing still is definitely not a problem with the magnus line as long as you aren't spamming your shots constantly, reloading is where the big issue of standing still comes in.
You may have issues with wolvers and gremlins with Valiance, so as long as you're just using your sword for those enemies then you should be fine with the blaster series.