Welcome to the forum. I'll let others chime in on the pro's and cons of a class B v's others, but from a chassis perspective, my wife and I faced this question starting last year when we started looking for a camper based vehicle that had an engine (owned an older popup before). I wanted a Sprinter from the fuel economy perspective and the fact that they are massive inside, however, Sprinters have a regimented maintenance schedule, could be costly to own using only Mercedes spec oils etc, and sometimes have issues with their emissions systems, particularly the newer models that have the Diesel Exhaust Fluid (DEF) systems installed (2008-2009, I believe). Because of this, we bought a Roadtrek on a Chevy chassis, mainly because when you're in the middle of nowhere, just about anyone is familiar with a Chevy. We traded fuel economy for less possible downsides that the Sprinters have when an issue comes up with the emissions systems and you have 10 starts to get it to a dealer.
We love our 2008 Roadtrek mainly because it's about the right size for 2 people, easy to drive, and especially easy to park. It does take up more than one length of a parking spot and our 210 is a little wider than the standard Chevy Express van chassis it's based on, so finding a spot a little further out is a good idea, or backing into a stall so that the overhang past the rear wheels is over a grass area v's pulling head in and the back of the camper hanging out. You get used to it, but mostly manageable in single stall parking spaces with some exceptions.
I would suggest searching for some key words or phrases on this forum and start to read and see what others have to say. You'll probably learn a whole lot in the process as there's a ton of information here.