I know the mods these days have moved to VV, VW, LCD's, Regulated Power, etc..., but I have had a Chuck for over a year, and I vape 6v all day long. I've only had to change the switch a couple of times, which is very easily done with a solder iron. I have the option to vape @ 3.7, and now they have 4.8v batteries, but if you enjoy 6v, what's the point of VV? You might say," all the different resistances of the atties or cartos", but all you hAve to do is find the atty or carto that suits you and get those. Order you some lr's for your 3.7 dripping, and your regular resistance cartos for throughout the day. I have the Chuck and Saber Touch, but I steer away from all the gadgets. Too many parts to break down, and everything eventually breaks down. The Reos look nice. Not too much gadgetry, and the feed pump, and even the switch is mechanical. Which means less chance that something will go wrong. If you are just looking at your list, I vote Reo.
Though I agree that all mechanical mods offer more comfort as car as durability goes, that can't be the main factor in deciding.
This is the was I see it. You have 24 months of hassle free Darwin use under warranty for $230, or less then 10$ a month. Everything that happens after is just bonus as I see it. Yes it's not bomb proof like a SS Super-T or somehing, but the vape more then makes up for it. The cost factor for most of us ex smokers should be the least of our worries IMHO.
So it's nice to say you vape at 6v's all day and love it. But would you really be at 6v all day if you could change it in seconds with the flick of a finger? I'd be surprised if you did.
This mod will allow you to try 3.7, 5v, 6v and anything beyond or in between, with any carto/atty setup you can think of. I have a bendy gooseneck on mine so there's no limits to what I can stick on it lol.. Even beter then that, it's bloody easy to use.
I thought I wanted a tube mod till I tried the Darwin. This and the reo seem to be IMO the way to go, especially as a first mod. I still want a reo and will own one soon hahaha, but Darwin just does it all, and if anything you can use the Darwin to dial in what you like before you commit to 3.7 or 6v stuff.
Ramble over lol.. Just buy what suits you best! Good luck!