Well, let me throw my 2 cents in here now that I have had both for a while now...either way you can't go wrong, they are both really good. I still favor the Darwin for it's versatility and pocketability (making up words now), but the Provari is a monster as well. Sometimes you just want to sit on the couch with a good old tube style mod and the Provari suits that well. I have run into the current limit on the Provari with a LR carto, so the Darwin wins there but really there's no need for LR stuff with these mods. I could easily recommend either one, although I'd lean towards the Darwin if I had to pick just one. It's a little more versatile, simpler to use and charge, and I actually like the swing arm.
Just my 2 cents, ymmv. Enjoy!