The 235 will be better under given circumstances, IE packed snow on hard surface. Very common on snow covered roads.
reason for this, the 235 is narrower, so your total vehicle weight is on a smaller contact patch, therefore more pressure applied in that area. This improvement is more noticable on 2wd vehicles because they don't have the benifit of the front wheels pulling them through.
If you're talking deep snow, then the wider tire will be better to help get you up and over it. Personally, I like the skinnier tires better because 90% of my driving is on roads.
for the tread, softer rubber stays more pliable in sub-freezing temps, so you get the extra "wiggle" of the tread block to help the "gription" on hard pack and ice. Of course, the more sipes the tread block has, the better the "wiggle" gets, and the better the "gription" gets.
Todd