There are a lot of good combo's out there. You can really spend as much as you want depending if you go auto or pump. I think you see more 870's because they are readily available and cost very little and shoot very well. There are also lots of add on options as far as stocks and such for the 870. On the flip side, the mossy's, benelli's, and 1187 are all great 20's and all put up great numbers. Good luck and welcome to the madness!
Tim