Curtis, some of the basic differences between the Fred and the DPs. Your pushers will be on a heavier chassis and can carry more weight. This translates as a practical matter into more fuel, water, bigger black & grey water tanks is you plan on doing some boondocking where these items will really come into play. It also usually means that you can carry more of your "stuff", whatever that means in your situation. The DPs will normally have one or two pass thru storage bays where the Freds will have compartment storage in the slides and other non-pass-thru sites which limits their capacity and the size of items they will carry. DPs will have air ride and brakes resulting in most cases a better ride. The DPs will have a greater towing capacity.
You can get more and higher quality amenities in DPs (depending greatly on price). Bigger refrigerators (up to residential size), bigger beds (I don't believe you can get a king size in the Fred), hydro hot heating with unlimited hot water and engine preheat, and many other items.
DPs will normally cost more than Freds. However, some high end Freds and cost as much as some entry level DPs. The top selling DPs in 2007 were 1) Tiffin Phaeton, 2) Fleetwood Discovery, & 3) Tiffin Allegro Bus.
The key is to find the floor plan and storage arraignment that works for you within your price range. There are great coaches by many manufacturers in gas, Fred, or DP models. Take your time, look them over very closely, and you'll find the one that's right for you. That will be a Happy Day