If you have life charms in your inventory, then max block is more effective than pure vitality. If you have 7% MF charms instead, then going for max block actually makes your character have less effective life then if you just went all vitality. You get 11+% block for "free" anyways.
Anyways, to answer your question, it doesn't really matter, and there is much debate. I think frozen armor is the best because if you get mauled by Fanatic Death Lords, at least it will freeze them every half second or so.