Vapor World has been my go to and for a device I recommend the Uwell Koko (Keep on keeping on). It's small with pretty good battery life, and durable. I'm on my 2nd one only because I lost the first. It's been dropped out of my work truck countless times because I forget it's in my lap (big box truck so about 5 foot drop) and it just keeps on going. Coil life depends on what juice you use. Just a neat little unit that's never done me wrong