Well.... those are two of the very best atties available today.
Some thoughts:
* Build ease goes to the Derringer. It's not that the Nuppin' is hard to build on (other than the learning curve on the neg legs), it's just that the Derringer is ridiculously easy.
* The Nuppin' hits harder (feels like .1ohm lower resistance on identical builds), but the Derringer vapes hotter.
* Manufacturing quality (if you get an authentic Derringer, don't know about a clone) is a draw - both are excellent quality.
* Neither leak to speak of.
* Air flow control edge goes to the Nup' - I'm just a bigger fan of the 'straight' cyclops afc than the 3 holed design of the Derr, plus the separate afc ring of the latter gets messy and introduces another o-ring to manage. Not a big issue for me, but it is what it is.
* Nothing squonks and drains better than the Nuppin', although the Derringer (via CH) is fine.
* Some dt's look a bit odd on the Derringer as the cap has a raised lip, so some with OCD will be more restricted in choice. Also, the short cap of the Derr might introduce a shorting problem with some ss dt's.
* Build possibilities are prolly greater with the Derringer - it's straight forward post system (slots in the posts) allow for wacky wire configs (e.g., triple twisted, MM, etc.). I haven't seen the Nuppin' pushed as far.
* Flavour production for both of these atties is excellent - not much to choose between them.
* Aesthetics are so subjective that I have no opinion there - some folks like the unique lines of the Derringer, other don't like 22mm atties because of the overhang.
IMHO, these two atties are best of class for vapor/flavour balance and great for ADV'ing. You wouldn't go wrong with either. If I could only have one, I'd honestly have to flip a coin.
... but I'd prolly break down and get both