Like Zippy said - stay away from the 28ga ....that's not what you want...
$ 500 for a good Rem 1100 is a pretty good deal / if its in very good shape, screw in chokes, etc ... and yes, I think it will probably be a better long term gun for you than a Ruger O/U. A Rem 1100 will easily last 250,000 shells if you take care of it - probably longer.
However, I think the Ruger O/U's are decent guns as well / and will probably give you a 25,000 shell life before you have a bunch of issues with them ....but the fit and finish on the Ruger's hasn't been that good in the last 3 or 4 yrs / but they are made in the US according to their website - and I think you'll be able to get parts and get them rebuilt fairly easy. I think the Ruger is a better gun than many of the import O/U's like the Baikals, CZ's, TriStar's, etc ....