I'm a fan of Benelli semi autos, and I'm sure their pump action is good too (don't own one...). That being said, the 870 is really a no-brainier. It's a tried and true design, slick action, fair price/good value and it just works, and works, and works, and.... You can also get it in many configurations, from tactical to field gun to sporting to really fancy. And, oh yeah, it's made in USA.
My vote is the 870.