I think when one answers this question they must frame their criteria for "favorite". I tend to keep cars a long time and to high mileages.
Based on total ownership experience (how much it cost to own, how many miles I got out of it, and how much it breaks or broke):
1 - 2006 E90 325i
2 - 1988 E30 325i
3 - 2008 E86 Z4 3.0si Coupe
4 - 1997 E37 Z3 1.9L roadster (still have the James Bond license plate for it - BMW delivered them that way
)
5 - 1982 Ford Escort
Based on Best liked to drive:
1 - 2008 E86 Z4 3.0si Coupe
2 - 1997 E37 Z3 1.9L roadster
3 - 1988 E30 325i
4 - 2006 E90 325i
5 - 1972 Ford Pinto 2.0L (was most excellent for bootlegs)
The E21 320i fits in here somewhere, but I never owned one, just drove a few a lot.
Since someone brought up scooters (favorite to ride):
1 - 1990 Honda CBR 1000F
2 - 1994 Kawasaki Concours
3 - 1982 Yamaha Seca 650
4 - 1999 Honda Valkyrie Interstate
5 - 2019 Indian FTR 1200S (hoping this will move the CBR to number 2
)