Noting that I only know from pre-E46 M3s, IME the two cars are *so* different that after you have some seat-time in both you'll know which one you prefer.
But I'd sure prefer the Quattro in the winter, and it's not like I dislike RWD cars (with snowtires) in the white stuff. I can basically *ignore* winter conditions in Quattros with snows but the M3 would make ya *work*.
IMO the performance differences between the two cars aren't anything compared to differences in the software behind the wheel
Guys in *FAST* cars get lapped by people in *slow* cars all the time. (Yeah, I know, some cars are still a lot easier/more fun to drive hard anyhow, so it gets back to personal preference. Buy whichever you like best.)
Oh, and give some thought to who will service it, there are a lot of shops I wouldn't let touch my car.
FWIW, if I didn't already have a fortune in my E36 M3, I'd buy an S4 ( '04-'05/old grill V8 model).