Best advice i can give is try them all out. Personally, i shot an etek 3 because the only place that techs guns within a few hundered miles is an eclipse dealer, and damn i loved that gun. Id recomend it!
I like Snipers, as Coenen said...
You can buy pneumatics and an electro triggerframe and have a semi-auto if you don't want to play pump. The problem is, it needs to be re-timed every time you switch between pump and auto.
For simplicity, though, I'd take an Axe.