To be honest, I wouldn't go with either of the Autogun lines. To give some backup information so I don't sound like I'm pulling this stuff off the top of my head, I'm a 5* gunslinger (using the Nameless set) and I've used every line of gun, and many 5* guns. I haven't used a 5* autogun line, but there's a clear reason for it.

The range and spread of the autogun series is so short and so wide, that you'd only do good damage point blank, meaning a sword would be a more obvious choice. Standing still is the killer part of the gun, as it will almost always leave you open for attack unless you are far away (thus doing very tiny damage). The way the gun works is you press the fire button once, and it will shoot a 6 bullet volley (you cannot move, turn or shield during this).

If you really want to use one of the autoguns, go with the pepperbox series. Since the Needle Shot lines are piercing, they will be good against Fiends and Wolvers. Wolvers dodge so often and constantly (invincible while dodging I might add) that by the time the 3rd bullet reaches them they are already behind you nibbling at the soft part of your back. Fiends rarely stay still long enough for the full volley as well and them throwing things all the time means a guarantee you will get hit while firing.

The Pepperbox's charge pulls the enemy toward you, which can be a bad thing. If a lumber is in the attack animation and you start pulling it toward you it wont stop the animation, meaning it will hit you. But if a pesky zombie is inside some spikes or one of those totem areas you can pull him out of there instead of walking up to it and baiting it out.

All in all, I would recommend the Blaster series if you are only going to use one gun. Normal damage means you won't have to worry about what enemy you are fighting, and it's decent enough damage to get you by.