There are disadvantages to both but if those were my only choices, I would go with 285/35 without a doubt. 265/35 is too short for the rear. You should use 265/40 for the rear (stock size). I don't like the idea of running a shorter tire in the rear than the front (245/40 is taller than 265/35). 285/35 is wider than ideal for winter use. I am not as against this option considering you will still have winter tires and you live in NY vs some of the more snowy regions of the country. I ran stock sizes on my OEM 18" wheels when I lived in MN without problems except for deep snow. The 265/40 in the rear did not have enough traction to overcome the friction of the car plowing through snow greater than 5".
'13 M3 - Silverstone II - Sold
'04 M3 - Jet Black - BBS E88, KW Clubsports