Condition is key when it comes to used RV's. You can tell alot by speaking with the owner, and looking at the small things. Decals faded? are there any hack job repairs visible? Is the owner knowledgeable about RV stuff? Look under the unit for rust. Many RV's only get 3-4k miles per year in the summer, and otherwise sit. If you can find one of the queens you can get a good deal on a nice motorhome that will last as long as something bought new.
Age? I dunno. Sounds like you are looking at new enough units for it not to matter. The 6 spd is a bit better than the 5 spd, but not significantly so.
I have the old 4 speed and it does great.
It's really all about individual unit condition.
I personally ruled out Coachman, but I was looking at much older units (2003-2005 range). Winnie's are nice, but I saw some beat ones too, so you never know. ANY signs of water leaks or delam, walk away.
I ended up with a Fleetwood, and it's a good rig. Mid level quality, rubber roof, but all the appliances and stuff are pretty much the same on all manufacturers. Mine was barn stored and in good shape with a new roof, new tires and new batteries, I was able to buy it from the acutal owner instead of a dealer so I got to speak with them in person about the rig instead of just a blind inspection.
We went from TT to class C and absolutely love it. No toad takes a little adjusting to, but we've been fine. And the family loves being able to use the house while in motion.