@riggers Let me give you my 2 cents. I have both 2014 VW Passat TDI SEL and a 2018 BMW 328d. So, the way the cars handle are very similar. The engines are quite similar in specs overall, the Passat engine vibrates a little less than BMW's N47 (think: BMW didn't cheat emissions. LOL. So their engines are not as "refined"). Now, the vibration inside cabin is very similar, but I would say BMW does better job overall in cabin comfort. With BMW, there is very little road noise, the diesel vibrations and engine sound are much less, I think a better insulated cabin. BMW also gets slightly better mileage (44-45 mpg vs 42mpg on Passat). But we are counting pennies here. Passat has a lot more road noise and sounds "airy" from the A and B pillars.
As far as interior comforts, BMW BAR NONE! The infotainment is responsive, quick, works well with Android (with some coding to enable OFFICE features to read and dictate SMS and emails) but comes with Apple CarPlay, which is awesome if you have an iPhone (I don't care for these! Android fan here). The seats are more comfortable, I can go hours in BMW without booty hurting - Passat makes my booty hurt in about 2 hours. BMW trim I have has deep bucket seats, which is nice when I got psycho making sharp turns. The ZF transmission in BMW is buttery smooth. DSG is good, but more "sporty" feel - hence rougher up and down shifts. Quicker and sportier, but rougher than BMW's ZF.
Drawbacks of BMW - SMALL, very small. I regret not buying a 2018 540d with a 6 cyl diesel. But then I would only get 30-35 mpg and I rack up good miles each year! Look for 2018 540d if you're looking for a midsize diesel, more luxurious and more refined too. Remember 328d is a compact vehicle. The rear room in Passat can accommodate a giant, I cannot put a child seat in 328d without moving passenger seat slightly forward or placing child seat in the middle (i.e. unapproved location). I cannot fit it behind my seat, I am only 5'9 and some change.
No matter the decision, here is what I recommend. If you like rear space in Passat, you will find 328d much smaller. Front space - about the same, really not significant. Technology - cannot stand RNS510 (slow and buggy) in Passat. My 328d has large screen, responsive, head up display, blind spot monitoring. Passat is bare bones, although at SEL trim level. I hated driving Passat after the "fix" --- fuel economy dropped, the engine seemed laggier, overall not comfortable, acceleration terrible. Whether you get BMW or stay with Passat, spend $500-1000 and get a KermaTDI tune. It will basically return your car to a pre-fix level (nice and refined!) with a better handling and responsiveness. With Passat's engine AND DSG tunes, the acceleration even in 6th DSG gear will be awesome! Absolurely awesome! I am not saying I got the tune on car I have, I just have an experience driving with Kerma and without Kerma, and the difference is SIGNIFICANT. Passat is in the family (but not my primary car anymore, it got replaced with 328d). Passat cost me $33K brand new (minus TDI settlement, around $7k). 328d ran me $42,000 brand new. Happy with both cars. But a tune on Passat is an absolute MUST. Tune on 328d is STRONGLY recommended. Kerma is the way to go, I have done a lot of research on all of those, and Kerman keeps everything bone stock, car remains emissions compliant!
Now a disclaimer: I like cars brand new, since I maintain them myself and don't want to get someone else's project, so my diesel future is in question once my diesels need replacement. Praying for current administration to bring gas prices back to $5/gal and hopefully diesels will make a return given their efficiency. Then I will gladly finance a new BMW 5 series diesel. Goodness, I wish we could have a 4 cylinder 5 series, that would be my dream - comfort of larger cabin with economy of a 4 cylinder. Until then, hoping my good care of my 328d will give me many years and many miles of great performance and reliability, so far 60k on 2018 328d and 110K on 2014 Passat. Knocking on wood, mostly minor fixes. I maintain both myself, follow recommendations to the last drop.
Best of luck in your decision