psshhhh for me my favorite is easy
hard corps on the sega genesis babeeeee
I always have a hard time attributing any "favorite" game in a series to the Genesis. That system always seemed to lag behind both in graphical and sound capabilities. Granted, I think the inferiority of the hardware , compared to the SNES for instance, forced Sega devs to innovate with better ideas for games compared to Nintendo devs, I rarely have any favs from the Genesis.
The only exceptions I can really think of are Streets of Rage--graphically not as sharp, but made really good use of the soundset of the system, I play that far more than I do Final Fight. I still like Quackshot for some weird reason, too. Tazmania was also better than it's SNES counterpart, too.
I generally preferred the TG16 or even original Master System in their own time periods. But that's just me.
Gameboy Contra was cool, too.
Still , gotta lament the death of the series, no matter what the fav is...