My favorite bike ATM is a 32 lbs Al 29er with a chromoly fork.
This has more to do with it being a flatbar upright and very comfortable since my last crash that aggravated rotator cuff injuries.

My favorite bike before that was an 853 steel crit bike I crashed on (great ride quality).
My favorite bike before that was a fully carbon dropbar endurance bike (light/responsive).

It is the sum of the components, frame/fork materials, and fit with me and current injury status that decides my preferences.