Hmmmm, What is the best hammer? What is the best car? What is the best e-cig? Not really a right or wrong answer to any of them. It all depends on what you are wanting to get out of each. For me, a framing hammer works best for what I use hammer's for. For me, a sub-compact manual transmission car is best. For me, a variable wattage mod with a Rebuildable Atomizer Tank (RBT) works best.
I research a lot of stuff on mods, cartos, tanks, RBT's and RBA's (rebuildable drip atomizers.) I watch a LOT of video reviews on things I think I may want to try. Heck, I watch a lot of videos on stuff I don't think I may want to try, the reviews may change my mind.
If you have the money, buy a few things and try them out. If you are like me, and don't have the cash, ask friends if you can give their rig a try (I only let friends who will use their own drip tip use my setup)
All in all, the only person who can answer the question "What is the best e-cig" is you. Happy trails.