All depend on the kind of water you go to be diving in. Is not the same a 24º swim than an excruciating 3h dive in 12º!
The slick inside have more flexibility and properly cut will fit better: that will achieve more insulation, better mobility and ventilation.
On a two piece you don't have any zipper: little area for cold water exchange and no hard spots.
A slick outside achieve better hydrodynamics on the water, and you don't freeze down on an 36 knt boat ride... More flexible but so fragile.
Have a look on the Elios web page they have good explanations (do a search on the forum: is plenty of threads).
__________________
What doesn't kill you, makes you stronger... 
|
