One of the big advantages of a Class B is that drives pretty similar to a large SUV or other car. I don't have any problem keeping up to highway speed on the Interstate, or with winding rural roads. I'm in Northern Virginia, so my RV trips usually begin on I-95 - not that bad in the Roadtrek. Being able to park in my driveway without blocking another vehicle is a plus, too. Same for the relatively good gas mileage. Obviously, there are trade-offs, but they work for many.
Check out the Class B makers websites to give yourself a good idea of the options. Posting on the Class B Forum might help you down the road, there's often a fair amount activity and quite a bit of information.
That said, sleeping 3 in most Class B isn't a great option. Have you looked at the small Class C's, such Leisure Travel Vans Unity model? That has a twin/king bed in the rear and a single bed in the dinette. I think it's about 24 feet.