The Darwin is a great device, and with current price it's near a complete set provari (battery, charger, extender), variable wattage and all BUT it's never available anywhere while a brand new Provari is always there to buy. I am tired waiting for a darwin to be available.
The GGTS is a piece of art, and hardly available, not a vv & not a vw. It's a life time mechanical pv. With recent plan from Imeo (the maker of GG series) it will soon become available to anyone (hopefully). Sure it's not cheap but when you hold one, you'll understand why it's a great pv.
I love my provaris, and still dreaming for my own GGTS.
Everyone has a different taste though. This is just my opinion.