If your planning on travaling the US then I would not go any smaller than a 30'.Class A if your comfortable driving one, it will offer the most in-transit room. If the Class A is too much to handle, then definitly a Class C would be the next and would be the way to go. They are quite nimble in getting in and out of tight spots.
If you go for one with a slide make sure that you can access all with slide in, otherwise you might need to extend the slide in order to gain access to drawers, closets, bathrm.. Kinda hard to do when cruising down the road
I argree with the diesel test drive, once you go for a test drive in a DP, all other RVs will pale in comparrsion.
We started looking to replace our 30' class A gasser with a 34 to 36ft class A gas. The family called it the Great American RV hunt. We searched and looked for about a year before finding the one for us.
Ended up buying a DP,it wasn't what we planned on buying, but the options and the price drove us to buy it.(and I made the mistake in test driving her)
If you buy from the dealer, make sure you check thier reputation as it seems quite a few dealers will tell you whatever you want to hear until you sign papers. It wouild also be smart in checking with the local BBB. Make sure that all agreed on; is done to your satisfaction before accepting it
Good Luck we went from a TT to a class C to a Class A, and will never go back to the TT(although maybe a fiver)