Depends on the ultimate use. If you plan to rip out the interior and do a camper build, then why pay for, or deal with a nice interior. Start with a base model. If you want to spend your money on the conversion, and still have a nice interior for road trips, then get the Chateau for sure. It has nicer interior panels with cupholders and bins, plus many have rear captain's chairs.
As far as mileage goes... If you are looking at a 6.0, regardless of the mileage, plan on spending some money right up front to deal with the usual suspects. Do a EGR cooler delete, replace the oil cooler, and get a tuner. Early model 6.0's also have some issues with the wiring harness getting chaffed and eventually shorting. I think 2006 and newer have better protection for the engine harness. Maintenance records should be a key factor when looking at the 6.0. A well maintained family rig would be a nice find, but fleet maintained vehicles can be just as reliable, however the chassis/body tend to be more worn.
The 7.3 has it's own quirks, but many agree it can be more reliable at higher mileage than a comparable 6.0. Problem is, they are hard to find. The 6.0 is often sold at a discount due to the reputation that engine has, so you may get into a nicer vehicle overall for cheaper. I would just stay away from higher mileage, say over 120k, on a 6.0 without any knowledge of the maintenance.