The Airstream Westfalia was the first B we looked at. I liked it a lot. That climb to get in bed was the main factor for passing on it. The other factor was when we looked at it at a dealer the salesman couldn't demonstrate and pull out the lower bed. I get pretty impatient when a salesman can't show you something or answer your questions. In Europe that similar design is still being sold as the James Page.
Most Sprinters have the 6'-3" headroom. I know a few tall Sprinter B owners and they seem to handle it well. The headroom is pretty clear from front to back with the exception of the 2" air-conditioner intrusion. The other positive factors of a Sprinter are the level floor from front to back, the upper cabinets are not head bumpers when you sit down on the sofa or bed in the back or getting in and out of the cab seats in front, and the sliding door is tall and easy to enter and exit without bumping your head as you may experience all these in a RT Popular 190.
As far as aisle width goes for Sprinters, the Great West Van Legend probably has the widest aisle at a minimum of 26-1/2" clear at its narrowest point front to back. My wife and I can easily pass by each other with a little bit of sideways twist. Most Sprinter Bs one has to wait until the other passes.
Davydd
2021 Advanced RV 144 WB 2500 Class B
2015 Advanced RV Ocean One Class B