I can't offer an opinion on the gas versus diesel MH as the only type of RV we haven't owned is a gas MH. I can say that the only thing we will have from here on out is a Diesel MH. Our first was a 1999 Discovery and it was amazing. Our second that we just purchased is a 2005 American Tradition.
The 1999 was mechanically and structurally sound but needed updating. Floors, tvs, upholstery. Decided that we would rather put that money into a newer unit. Started in the 2012 - 2015 range and after a year of looking decided that the 2003 - 2008 models offered alot more bang for the buck.