I'm in a similar position (I have a 20ft Toy hauler/Transit) but have
been looking at a Class C or B+ for a couple of cross country trips.
This will be for my wife and myself; I've been looking at max 24ft.
Easier to drive and able to get into tight spaces, easier to park
at shopping malls.
Diesel or gas - don't think it makes much difference for me. I looked
at Mercs - very nice but the diesel Transit has caught my eye. Why?
if you breakdown in the middle of nowhere there is always a Ford dealer nearby.
I prefer a slide-out for the extra room - I've never had a problem
with my slide out on my older TT. Also you get tend to get a better
sofabed with the slide out and room to move around.
Axis or ??? : I've looked at a couple of Axis - you do get a lot of RV
for the money. The Axis is on my list as I probably won't keep the
RV for more than a couple of years; I still prefer a pull behind TT/TH. I was not TOO impressed with the workmanship/quality but then
it's built down to a price; The mechanicals are all FORD.
One item to think about. A Class B/B+/C will have to be packed up
each time you want to go anywhere (like the local restaurant).
Unless you are willing to tow a car - which kind of defeats the
object of buying a small RV....