What is better the v5 bcd tank or the v4 bdc tank?

i have had a bdc tank mini before from totally wicked, and i have a few of the bdc atomisers, i broke the old one and want to buy a new one, i noticed there are three bdc ones now, the v4, v5 and the one called bdc tank mini, i don't want the same one i had, so what should i get??