I have had 2019 Transit (130", medium roof) and switched to high roof 4x4 144" Sprinter. I like driving Sprinter much better. The steering is a lot more precise and less tiring at high speed, fewer corrections required. It feels more secure on interstates at 70-85mph. The Mercedes has amazing brakes. I love those brakes. Brakes tend to be tricky for car makers, Sprinter brakes are better than any cars I have owned.
Transit, perhaps due to its short wheel base was doing bucking motion on a concrete paved road, like i-25 north of Denver. After 50 miles my lower back would start hurting. It was so bad, I had to avoid this stretch and take back roads. Sprinter seems to be doing fine there.
I had the most basic large 3.6 engine in the Transit, lots of power. The engine in Sprinter is of course slightly weird with its late turbo pickup. I do not care about the engine much though. Seems to have enough power to pass somebody doing 70 on a two lane road, what else would I want?
I preferred the cab ergonomics in Transit. Better visibility, light interior, better elbow support. For a van owner, Sprinter is nicer to get between back and the driver seat. All the electronics in Sprinter I would rather not have. Just give me traditional parking brake and gear shifter. Electronics scares me, reliability wise.
All in all, in my opinion Sprinter is a better driver.
Talking about 4x4 vs RWD is probably not fair, but it is a necessity, in my opinion. If you plan to ever take the van off pavement, even on an occasional dry dirt road, summer or winter, AWD/4x4 is a necessity. I think front wheel drive (RAM) probably would have been acceptable, but RWD is just no good. In winter, no tires, even studs solve the RWD problem.
I love the ground clearance in 4x4 Sprinter (although not for getting in and out!).The AWD Transit has the same clearance as RWD. I totally get now why Ford did that, it's a real feat of engineering. But for those of us that want to take the van off pavement, even just to pull off a side of a dirt road to camp on forest service land, the ground clearance is very important. MB 4x4 system is insane, why do I need to fiddle to engage 4x4? Just make it work with a button or a shifter, seriously!
I do think that Sprinter is a better quality build than the Ford. I would describe Ford build as a "budget lawn mower". The paint is better in MB (significantly!). The parts fit better. The spot welding inside is better. The Sprinter does not cut corners on things like wheel well liners, mud flaps or any other things you would expect in a modern vehicle. Less crappy plastic under the hood.
Transit feels like Ford left out anything that would not contribute to driveability for however long the van is typically leased by a commercial outfit. If a part does not affect speed, it's left out. This is not to say that MB build quality is good either. Sprinter is not a Honda or a Subaru, but still much better than Transit.