I wrote this on a YT video comment:
They are both good very good vans. Comes down to personal preference / needs for the most part. Transit PRO: * more engine choices * more roof height choices (the medium roof is 6' inside, an overlooked option for average and shorter folks) * more popular = more peer knowledge, US aftermarket support, more used Transits for sale * mechanical limited-slip differential option due to RWD * better towing due to RWD Transit CON: * backup camera in the door so you can't see if you are backing up with the doors open * relatively short wheelbase for vehicle length * least ground clearance of any fullsize cargo van * costs more Promaster PRO: * very wide. 4" wider at the bottom and more like 6" at the top since it doesn't narrow significantly up top. * more cargo volume at every length * better traction due to FWD * lower cargo area due to FWD. This gives 10" more headspace for a given roof height * commodity engine and trans (3.6l pentastar, 62TE trans) easily sourceable * .9" more ground clearance than Transit * better turning radius for each wheelbase * costs less to buy and operate: my TCO calculations show the Transit costing 6.7% more over 5 years (including purchase, fuel for base engines, maintenance, insurance, etc) * dominates European RV market = European aftermarket support (but can be expensive to import) Promaster CON: * only one gas engine option * FWD, if you don't like that * some folks don't like the bus-like driving ergos * rebadged FIAT Ducato, if you base your buying decisions on memories of the 1970s I bought the 159" high roof Promaster and absolutely LOVE it.