Wow, that's like walking into an Auto Show and asking "Hey, what's the best car!"
All you can get here are opinions. So of course, I'll give you mine...
I've spent a small fortune on Mods. If you are looking for flexibility, durability and classy style, in my opinion, the GGTS is the best. I love the power delivery of the Chuck and the ability to personalize (I have two), but the switch is a major anoyance, and having taken it apart a few times, the electrical soldeting is below my standards. The USB P/T feature of the Bartleby is great, but again, the feel of the switch is poor and doesn't give a solid off/on connection. My 5V box mod is great for delivering warm high volume vapor, but is bulky and has the same switch feel as the Bartleby. The GG slim is great for stealth
vaping, but only uses 3.7V, and the battery life on the small batts is terrible. The GG Super Slim gives you 7.4V, but has the same life problems, and at 7.4 V, you blow out any low cost atomizer fast. The GGTS lets you choose from a bunch of different battery combinations, uses four different atomizers (including you current cartomizers) out of the box, and has no electronic parts, so the reliability is far superior to everything else I've tried. I'm a hard user, and the GGTS is the first device I've owned that lets me walk out of the house with only it (and
juice) in my pocket. I can set it up with an 18650 battery, an i3 atty and a drip tip, and I can vape all day long without messing with battery changes, cart refills, or fiddling with the switch. When I'm near my supplies, I can use several different batt combinations and play with carts or cartomizers at will. Because it is made out of high grade aluminum, it's surprisingly light for its size (much lighter than the chuck), and the switch locks, so you can just carry it in your pocket without disconnecting the atomizer, as you have to with the chuck. It has great conductivity so you get a lot of power delivered to the atty, even at 3.7V.
The down sides are: The metal finish picks up fingerprints and dulls quickly, so you have to shine it up if you are concerned about the look (it looks fine with a dull finish, but it becomes a fashion accessory if you shine it up). The locking button assembly has a tendency to become unscrewed and need readjusted it you tighten it too hard (I've learned the "knack" and don't have this problem anymore). It costs twice as much as the others (or More), but in my opinion, if you are looking for a one shot mod to meet you long terms needs, this is it.
That said, I also have "IT" from e-cigmods on order (it will be my first juice box style), and I'm a gadget guy, so I'll probably keep on ordering new ones as they come out.
Hope this info is at least a little bit helpful.
