I owned a12gauge Rem 870 for a while, and it is most definitely bad ass. 28" barrel and a 5 round mag. I did add a 5 mag extender to it, as well as a few other goodies. Anywho, the 870 was my first gun, and I found maintenance, as well as adding cool guy parts, were pretty easy.
From my experience, the 870 is a pretty awesome firearm, stock or modded. Id assume a longer barrel would increase accuracy, as well as make it more difficult to get that "swiss cheese" effect around the house. Hahaha. I purchased mine for 330$ or something like that at walmart. Good luck mate!