I would go with the 870, although I recommend a Wingmaster over an Express. Both varieties are great guns, but the WM beats the EX as far as quality is concerned. Reliability is one of their strong points, as well as fit and handling (often a personal preference).

I'm using a old Wingmaster myself, but chambered for 2¾" shells. I've got it patterned out to 35 yards and I'm just counting the days until April 10.