Then it sounds like you are looking for just a coach to travel the country and not live in full time. In this case, I would look for the floor plan that suits your needs first and worry about the power plant second. Every coach will get you to the top of the hill while pulling a toad. Some will get you to the top quicker than others but that is more of an ego thing. I have had both diesel and gas and I have found that we spend more hours sitting in and enjoying the coach than driving it so the engine has never been that important to me. The idea of having a warranty on everything is important to many. The newer coach will have the latest electronics which may have to be changed on an older coach.
Another thing you want to ask yourself is realistically how long do you plan to keep the coach? If you plan on RVing for 10 years, and you buy a coach that is already 10 years old, how much longer will the aged systems continue to function? Look for comfort and functionality first and you should do fine.