Seat Quality - flatfour
Driving 50,000 miles a year I need good seats, currently Saab they are excellent, what other seats are good out there as I will need to change shortly and Saabs seem to be artificially holding prices of thier cars up.
Seat Quality - volvod5_dude
Volvo V70's and S80's and BMW 5 series have really comfortable leather seats IMO.
Seat Quality - Marcos{P}
My first Merc C-Class had beige cloth seats that were not only very comfortable but after 120,000 miles looked and felt as good as new. The leather seats in my new E-Class are supremely comfortable but I've only covered 11,000 miles so I couldnt comment on the durability of them.
Seat Quality - CM
If you can afford it (and it might be worthwhile if you do 50k pa) I believe that some of these "active" seats are pretty good. These are the ones that gently massage you.
Seat Quality - Morris Ox
May be this wouldn't matter to you, because you sound like you're in the market for a prestige badge, but you could do worse than have a look at a Mondeo.

Say what you like about Fords, but their ergonomics are spot-on: good seats, good relationship between driving position, steering wheel, pedals, main controls etc., all of which contributes to comfort on long journeys.

Value my car