My choise would also be the Mercedes E-Class:
1. Exterior Design. Clearly the E60 is very old and due to be replaced. It really needs the M-Sport Package to look competitive, but the new E-Class and XF are much more fresh. The Jag is very nice styled, but I doubt it has the typical classiness of a Mercedes design. It looks fresh, but not for long. The E looks great and it will look great for many years!
2. Interior Design. I am not a fan of the E60 interior. It looks very minimalistic in my opinion, and other BMWs have a much better interpretation of a minimalistic interior. On the other hand, Jag's interior is nice styled, but looks gold and strange with the yellow light illumination and the quality is a step behind the Germans. The E-Class interior is nice, yet it is not fabulous. It has a typical MB essence and is very ergonomic. It's of great quality, too. Among this three interiors, my favourite is of the next 5er...
3. Engines. It's not deniable that the BMW has the best engine of them all, but it's a diesel. And I don't think a diesel suits the BMW philosophy. I'd rather see a diesel in an MB, as it's a very comfortable cruiser, and a gasoline (N/A) engine in the more sporty 5er.
4. The 5er is due to be replaced, but I wouldn't care about it if I was planning to keep the car for long. But if a replacement would come in 2-3 years, then this lead to a smaller than normal resale value. Thus I'd prefer an E or a XF.
On the other hand: If this was between 530i and E350, I would choose the 5er, due to the superb driving dynamics and the very good engine.
