Who cares? Parts are interchangable! But I'd have to say the 89-91 cars are more refined and the styling never looks outdated. I always hated that black molding on the 86-88 cars. I've had a few S4's but now all my cars are Series 5. Three TII's: two 89's and one '90.

 

i havnt had much experience with 7's yet so ill just say the s5. then ill say 91 just cause its newer.

 

I prefer the 86 Automatic BASE,( lightest car)(Stock Aluminum hood)
equipped with:
5 Speed tranny swap ( no REDNECKED engineered mounts either)
88 TII 5 lugs and brakes
4.3 Clutch LSD
88 Vert Rims

 

Mines a 91 and i love her!