I'm mainly a gun user in the game, and the gun I use is the Sentenza. The thing that really got me hooked on the antigua series was the nice 5* charged attack, the pushback of the owl is great and I've even seen it hit the same enemy 4+ times, but also the 6 shot burst it has.
I probably should have gone with the argent, considering how weak the sentenza is against a lot of mobs, but I love the look and feel for the gun. Maybe I'm just choosing aesthetics over functionality and damage, but when paired with a gravaton vortex you can unleash hell.
The 2 shot guns seemed powerfull but I don't really like that playstyle, I started off with the blaster series but never upgraded to the valiance. Overall, I do love the sentenza, but it seems very situational. that being said, you rip apart wolvers and gremlins like no other ;]
It's not bad. At all. It just isn't good either.
The argent is a pretty decent gun as it does the same damage to everything.
Just don't expect to be on par damage-wise against the alchemers.
It still is a very viable choice.