You have a 1985 Rheem condensing furnace that has lasted? Not only stick with Rheem but try your damnest to get the same installer.
Not just Rheem, but all manufacturers of condensing furnaces in the 80s had issues. Rheem simply had a few more than I'd like to be remembering. Your unit must have been impecably installed and properly sized for it to still be operating.
The Rheem/Ruud modulating furnace is without a doubt the most comfortable furnace on the market. With less bells and whistles you can get a nearly comparable two stage furnace by any manufacturer. Of these, the Goodman GMS or GMV series or the Amana AMS or AMV series are the highest efficiency with the lowest price tags. The difference between the Goodman and Amana brands are the Goodman heat exchanger is aluminized steel whereas the Amana has the same heat exchanger in stainles steel. Also the Amana uses a better ignition system with a more durable ignitor.
Whatever you go with, have the contractor put in the two pipe, direct vent system. Most likely the Rheem you have is a one pipe vent using indoor air for combustion.