My first 12g was an 870 and I still use it for practically everything. There's tons of add ons, upgrades, and just plain cool looking parts and accessories (if you have a tactical loving side) for these. You can't go wrong.

I bought the 870 express magnum with a 28" barrel, synthetic stock, brand new at walmart for something like 240 bucks. Added a 10 dollar HiViz fiber optic front site and now it's pretty mean.