First of many questions on vans

[Kyz]

The RV is almost out of here. I have a buyer and he is scheduled to come get it on Saturday. He's had it inspected and it's all good and he has the check from the bank in hand (he sent me a picture of it). So now, I'm happily in research mode and soon to be in hunt mode...

What I want is a van to build out. I have help here locally too. So first question is...what van... 

Pros and Cons as I have read/heard them.

Promaster: pros are the walls being boxier, width is better for bed placement, generally cheaper / cons higher mainteance costs

Sprinter: pros are smoother ride, diesel, better gas mileage / cons higher maintenance costs, harder to find mechanics

Transit: pros are lowest maintenance costs, mid-range costs / cons (and this is a new thing I've seen popping up in the last few days) rust is worse

Please add your thoughts, etc. Dispute the pros and cons etc. I first wanted a promaster, then I wanted a transit. I may end up getting just what I can find due to availability. 

I'm also planning to travel in my RAV for a bit so I'm not in a super hurry, but it sure would be nice to start a build sooner than later. 

I would consider a Class B, but they are super expensive and I've yet to see one with a layout I'd even remotely like.

Pros/Cons to buying new vs used? (Warranty a concern?)

Pros/Cons to going with a build out vs an RV that I'm not thinking of? (I'm already aware that they might not be welcome in fancy RV parks, which is fine with me.)