The Foresters aren't bad, the Corollas are pretty comfy, though I have spent no longer than 5 hours in them, that stretch proved excellent. The Mercedes' were awesome, good for loooong days. Our old 1988 Mazda 626 had so-so seats, lacking a long enough seat cushion.
The 911's seats were easily the best of any car we've had. Firm and supportive in the right places, adjustable in a zillion ways, the only flaw was the leather was a touch stiff and the AC was tepid, meaning hot black leather stayed hot for far too long. However, the fuel tank needed refilling long before your butt needed a rest...