If I were you I'd pickup a cheap cross fork for the winter, and get some fenders. If you can only have one bike fenders are gonna be real nice to have for those wet days, and in the winter/spring the roads seem to be wet most of the time..

I live in brookline, and really don't venture to cambridge/sommerville during the winter so I can't say how their plowing is.. brookline and boston are both pretty quick; they do sand/salt quite a bit. FENDERS!

Jer