I don't think there is one "best" older model. It all depends on the prior owners and their upkeep. When it comes to used RV's it's really a buyer's market. There are so many used ones for sale all over creation. Many owners that are selling directly often price their beloved RV out of sight, then drop the price drastically as the months roll on and reality sets in. So even if you like one that is overpriced... keep their contact info... 6 months down the road you might still be shopping and they might have cut the price down to what you can pay.
Look at lots and lots and lots of models, even the ones you can't afford. This will help you come up with your short list of "must haves" and a long list of "wishful haves". Picture yourself living in it, sleeping, cooking, working, entertaining, whatever your lifestyle is. Buying an RV is ten times easier than selling one, so be patient and wait until you find one you really like, that you can afford that you can picture yourself living in long term.
I have owned and lived in houses large and small, sailboats, apartments, mobile homes and now a 1994 28 foot Class C motorhome for the past 3 years.
I am having a blast! Doubtful I will ever own a large house again, I love the simplicity of my little old RV. I am mindful that my clothes don't exceed the storage allotted. If new clothes come in the door, then old ones go out the door. I don't collect up useless junk but I have outfitted my kitchen for cooking at home as in my case, eliminating dining out puts a lot of gas in my tank.
The first year I managed to travel to 17 states, but this past year or so, I've limited myself to mostly the southeast, just soaking up what's available in this given area. Eventually I will travel far and wide again, but for now I am finding plenty of beauty and nature all around me.
I alternate between traveling, workamping and working part time for money. I love the idea of owning my own home and renting or borrowing the land. Workamping has afforded me some adventures of living in beautiful places while working part time in exchange for rent and utilities.
I paid cash for my RV, as money comes available I make repairs and upgrades to make my home more comfy and cozy to my liking. I try to keep all the systems working and the engine and generator functioning nicely. I seem to be perpetually behind on everything, but eventually most of it gets done.
Go look at LOTS of RV's in all shapes and sizes, work on your budget to figure out where you will camp or live in it, how much driving and gas and so on. You always have to be setting aside money for future maintenance if you are going to have any fun in it.
But after 3 years, if you divide my costs of owning my used RV against current rental rates for housing, I have made out like a bandit and been able to live in the places that appeal to me which are not the big cities, but rather places set in the heart of natural beauty.
It's not a lifestyle for everyone, many fulltime RV folks spend 10 times per month what I spend, but I needed a place to recuperate on a small efficient budget and this has worked out beautifully for me.