I guess i lied, i never did design my van in a transit 148 extended, only an updated long version i built previously (and also had on order) and was much different being a shorty. BUT, i did have the 148 extended transit here last week and did some comparison.
Transit 148 EXTENDED vs Sprinter 170. notice wheelbase and where that places wheel wells inside and ease to work around, sprinter wins here since they naturally fall under the bed area and transit in living area. plus the huge transit rear overhang/departure angle SUCKS. Also notice squareness of the body, both on the sides and up the back door, Transit wins.

but that also means the sprinter longer wheel base break over angle is not as good. front overhang is huge on transit where fairly short on sprinter. the perceived ground clearance difference is HUGE
The transit has a really short nose in comparison, hood length is very short and more motor is inside the van pushing seats back. Notice height differences in driver seat locations, high in sprinter vs low in Transit. Transit you feel like you are sitting in a car and driving a car, maybe an escape. Sprinter you feel like you are in a truck, sitting high. Those comments also work for suspension feel as well, transit car/sprinter truck. Me personally, i have driven trucks most of my life past a few sporty cars/wagons/sports cars. I'm more utility in my vehicle choices and prefer to sit high, so huge win for Sprinter for me personally. Its all opinion, but i think the sprinter just looks much better.
actual cockpit. i mention sprinter seats are much better and after driving still say that. The transit center council is kind of a pain to crawl past to go to the back. and since the seats are lower, you kind of fall into them. Dash, just kind of weird design to me. Sprinter seats are much higher, so high i built the foot box for vertically challenged wife 1.0. Dash better layout but must admit i hate the Mercedes MBUX "infotainment" system. Having owned many RAM/JEEP trucks with the awesome U-Connect, other manufactures should pay attention to someone who dies it right. But never tells Germans anything..... Also, Sprinter gear shift lever (looks like blinker stalk on the right side)....not sure who ever thought that thing was a good idea, but transits is kind of obtrusive.
Now the real nitty gritty, measurements. The sprinter is a complete build i did a while ago for a customer but showed interior better than mine so the picture i used. Transit was a partial for me, I just did the interior wall finish and sewing of things, customer built floor and cabinets. He brought it since he is changing floor plan for the 3rd time and I had to redo some things to match. I adjusted my measurements like if it was 100% finished the way i build, floor thickness and lower panel finish. so as apples to apples as i could get.

I was surprised the Transit was actually 1" narrower inside, but walls are MUCH thicker so outside is probably wider then. In a transit i can just fit an East/West bed in the natural window pocket at 74.5" vs sprinter max is 71. Transit you can just barely get away with no flares since 75" bed is pretty standard, sprinter have to do flares. I kind of prefer N/S if room allows, so moot point kind of. 3" height difference, ~9" usable floor length difference. transit more square to ceiling. wheel well location as i mentioned before. ALSO, Sprinter slider door is full height @77", transit door design is weird and is shorter @ 66.5" so always have to duck under it.
like i said, if for some reason i built another van for me it would more than likely be a sprinter, but probably a 3500 with super singles (i hate duallies). the extra capacity would be nice. I actually dream of building a chassis cab with a foam core box and flat bed, so....... Trying to sell it to wife 1.0-ha. Reality is, im 100% happy with my current build--just need to get out and enjoy more.