Diesel: More comfortable to drive. Heavier coach, so no road sway, no pushing from trucks etc. More stable coach. No noise when driving, you can talk to the passenger. Generally, more CCC, and more towing capacity.
Gas: You can buy a newer coach so you'll get newer appliances etc. More noise from the engine as it's under your nose as you're driving. Lighter coach so road noise is more pronounced. Less comfortable to drive. Less CCC and towing capacity.
Notice most of the difference is in the driving portion of your journey. So, depending on your situation, you have to decide which is best for you. If you 3-4 trips are short and around your S&B house then driving may not be that big a deal. However, going on long trips, the DP will win hands down. Add a tag and the difference becomes even greater. IMO, diesels tend to hold their value better than the gassers and many are better constructed.
Remember though, that the most important part of choosing a coach is not what it's powered by, but the floor plan that suits your needs. You'll spend more time 'living' in it than you will driving it. The best coach for you is the one with the right floor plan. Get one you like to drive that your wife hates the floor plan and you'll never be a happy camper......Dennis