Emil, get an 870. I find the 3" guns have no issues. Some of the supermags seem to have problems. Ive seen every shotgun fail at some point, but my 870 has been flawless since day 1. You really cant go wrong.
Even if there was an issue, getting parts and service is easy.
Mine has been thru hell and back, and I dont take very good care of it, and its never let me down. Ever.
Ive hunted with lots of guys, with all the fancy shotguns you could think of, and seen them all turn into a single shot in bad conditions, but my 870 goes bang, bang, bang every time.
If I was you, id be looking for an older, used, 870 wingmaster. No need for 3.5", you will kill just as much game with a 3" gun, trust me.
S.