Is there a 'I wouldn't buy a ? Motorhome' - and why?

Newmar and Tiffin are both well built. I can speak for Tiffin that they have taken good care of us over our 4 years of ownership. Would not hesitate to recommend either. Assume you are talking diesel as Phaeton is diesel only. That leaves you with Cummins in anything recent. Again can;t go wrong. More power may be better, especially if mountains are your thing. But we have experienced underpowered (gas) going over the mountains and for the most part there are pullouts and multi lane stretches.