As mentioned there really isn't a prime season. You will found a larger selection during Spring and Fall when owners are trading in either before or after the summer travel season.
Concerning manufactures you'll find that brand loyalty is very strong so opinions will be all over the places. I like by budget model 2006 Hurricane. Never left us on the side of the road or caused us to come home early because something broke. Very basic coach but easy to fix and light rolling weight but some owners will complain about fit and finish or light weight cabinets or other items they consider substandard.
Years to avoid? Newer than 2008 has an advantage with the entertainment systems (digital TV). Fuel injected gas engines are better than a carburetor but you'll have to go back maybe 20 years. Each new model year brings advantages over the last with improvements. Bigger more fuel efficient engines, more gears in the transmissions, better roofing material, no carpet or less carpet in newer models, wider wheel base front axle,,,. Go out and look around and once you pin down a model and year ask the question again.
2006 Hurricane 31D built on a 2006 Ford F53