Would like a recommendation on replacing Rheem Model RC8A-6089GG243 with a quieter, more energy efficient unit. Any suggestions?

All the late model hvac units are good. The biggest problem with any unit is the install. A great unit can be turned to junk with a bad install. You should get 2 or 3 estimates from local contractors since not all brand names are available in all areas. This is the main reason it is difficult to recommend a specific unit. They all work well and heat well if installed correctly.

Then check with the BBB and your neighbors as to there recommendations for a quality contractor.