Opposing slides in the living area are a must for us. I personally prefer a used coach with a good history. We are presently work camping in a large park near Big Bend np. I have run into 15+ people on maiden voyages with minor to serious problems. This runs the gammet from high end dps to entry level tts. One guy with new Thor had 2 pages of problems, but cw couldn't get him in for 6 weeks!
Used rigs tend to have most of the bugs worked out. Most new rigs have a 1 year warranty, so your window for help is fairly small. If you unsure consider a service contract.
Jmho