We went with the Class A Toy Hauler. The Outlaw is the original (since 2007) and best selling with 2 floor plans. The Canyon Star's are very nice too (made since 2009) - also with 2 floor plans.
2015 Outlaw Class A Toy Haulers: Class C Motorhomes by Thor Motor Coach
Canyon Star Floorplans | Newmar
And there are others in the used market, see: Class "A" Toyhaulers
The reason we went with a Class A Toy Hauler was the versatility and options. The garage becomes a spare room when the toys are unloaded, your bike is safe and protected inside the motorhome, not bouncing down the road like on a trailer or exposed on a rear-end lift, and you can still tow a car and/or other trailer if you want.
The reason there are no newly produced Diesel Toy Haulers is because the engine must be forward of the rear axle to have the flat rear garage deck.
If you really want Diesel, there were some mid-engine Diesels made in the past, but they are rare. And, Front Engine Diesel's (FRED's) were offered in the Gulf Stream Bounty Hunter and the Damon | Thor Outlaw. These had the Cummins I-6 that comes in the Dodge Pick-up, but these chassis were discontinued and we are not talking 450HP monsters.
If you have motorcycles or have a need for a garage in your RV (dog breeder/show, workspace/office/shop from the road) there is nothing better. And there is really no financial reason not to get one now, with the used models like Outlaws selling for the low $50K's and used Canyon Star's coming into the market too.
Having said all that...if you must have the mega-HP Diesel Pusher then, sorry there is no Class A Toy Hauler made for you. And if you want an average to nice towable Toy Hauler, there's probably a new pick-up truck in your future.