We have an '89 Southwind that wer're happy with, but we'll be trading in pretty soon. Jimbo is correct: you really need to do a thorough inspection before you buy an older motorhome.
Maintenance over the years will make far more difference than anything else; year, mileage, model, chassis are far less important.
If the seller will go over every system with you and explain every repair and update he's done, and (hopefully) present you with maintenance records, you have a good chance of picking up a bargain motorhome that will last you many miles.
The sellers that tell you "the air conditioners just need a little freon" or "sorry, can't light the stove for you cuz the propane tank is empty" or "we never used the furnace but I know it works" are the ones that you run far and fast from, unless you're looking for a project and have plenty of money you don't need