We bought our first RV in 1997. We had been looking for a small Class C, my wife wanted the smallest available, she was scared to get a bigger one. Luckily when she was out of town I bought a new 31' Class C at auction but I got a great deal on it, dealer cost (he showed me). We kept the Class C for 11 years before buying our current coach, a 38' Class A DP.
WE decided we wanted to trade up and started looking, we went to RV shows, stopped at RV lots, and went to look at numerous used ones. We got lucky and found a really nice used "repo" in Florida. Got it for a great price, still probably worth 80% of what we paid for it 6 years later.
The advantages of a larger Class A is space and storage. The advantage of a DP is usually associated with power, towing and carrying capacity. The advantage of buying a nicer unit is the amenities, all the comforts of home.
Good luck on your decision
2002 Monaco Windsor 38 PKD Cummins ISC 250 8.3L
2005 Jeep Grand Cherokee w/5.7 Hemi