eVac vs Ultra-sil dry sack

I am in need of a dry sack. One for a sleeping bag and one for food. I was wondering what you guys think of the
eVac over the ultra-sil. I really like the idea of the eVac, but since it will compress by itself, I don't want my bag to get over compressed if its been sitting in the bottom of my pack the whole day. The ultra-sil will keep a constant volume. I'm not sure if thats good or not? Also which one would you use to hang outside?