while floating on the surface the back inflate will push your face down, so you need to keep fighting for vertical balance, the vest will provide more vertical and balanced floatation.
So you should question yourself: if you are going to spend time on the surface (vertical)...or below the surface (horizontal).
I, as a dive master sometimes have to assist divers on the surface, so I use the vest style.
Eco Sonora
I disagree with this statement. I dont have many dives but with my back inflation (Oceanic Excursion) I do not feel my face being pushed towards water. As said before if you get your trim correct then there is no problem. Over inflation will push you forward also. My BCD has 45 lbs of lift so I do not need to inflate anywhere near the max to float on the surface.