The new generation 808s are better.
If for no other reason, the battery life (then the standard 510 or 4081).
I use a 4081, its a dieing style. It is hard to find a good cartomizer for it. Its becomeing commen to find the 4081s in closeout status on supplier sites.
The 808 is sold by several venders as the primary system, not an after-thought like a 4081.
The 808 has seen recent improvements, the 4081, not so much.
The 510 and the 808 are the safer bet to find compatable accesories in the future.
For me, the 510 is out of the question as I cant stand manuals and Joye 510s are (in MY understanding) the worst offenders of what gave autos the bad name in the first place.
I curently use 4081s all the time now, but after trying out a friends 808, I just placed an order for a new 808 kit which I'll be cycleing these into my rotation to become my main PV in a few months.