I'm casually shopping with the intent of making the 5th wheel to class A jump someday. The question is a tough one and there really is not right answer. At this point I lean slightly towards new/newer gas. Repair costs and dated/used interior are the main factors.
There have been so many great creature comfort improvements over the years that I hate to go back in time. Old square TVs, dated furniture, fewer slides are all annoyances when looking at 10-15 year old DPs. The newer F53 chassis with the 6spd auto is getting some pretty nice reviews. The one thing I'd plan on putting some money into with a gasser is suspension upgrades. Many/most report the stock setup leaves a lot to be desired. A couple thousand dollars on bags or springs and sway bars and it drives like a whole other vehicle.
Of course, the DP has some great benefits too. It's just a tough decision.