We started with a diesel truck and trailer. When we decided to switch, we first started looking at diesel super Cs. After 6 months of looking, we came to two conclusions: we didn't like Cs as much as As and we sit more than we drive (160 hours per week vs. 10 hours per week).
So, the three most important aspects in an RV became: layout, length, and cargo capacity. We wanted a livable floor plan that suited us. This included an easy on the neck tv placement that allowed viewing with the slides in, a pantry, and a walk around king bed. We wanted an RV short enough that we could stay in our favorite parks - we are currently in a park with a 35' limit. We looked for a comfortable amount of cargo capacity - 2500 lbs. was too small because we needed the extra 1000 lbs. for batteries, solar panels, and water. Ours is 3500 lbs.
We have lived in ours for a year and a half and driven over 30K miles. We have looked at other RVs in the last year, including a newer version of ours and would not trade what we have now. We chose well, but it took a while.
You need to look at how you will use your RV, where you will be staying, and how you use your current house. If you will only be staying in full hook up private parks, your RV will be different than if you small like forest service campgrounds and dry camping. If you are a pack rat and like to take everything with you, you need something bigger with much more storage than a minimalist who carries the bare essentials.
At the dealer, if you find one you like, sit a while. Think of everything you want to bring and where you will put it. Try it with the slides in. Check the yellow weight sticker on each potential coach (we found some with an 1800 lbs. max cargo). Make sure you are comfortable in the driver's seat.
Best of luck in your search!