Hey Stl,
I think you will find there are some differences from one e-cig to the next.
Some of these are obvious - cart size, battery size etc, but on the other end, some may have a more pronouced taste, wet with flavor like a penstyle, while others like the 510 produces a more subtle flavor that emmits a dryer taste.
So the key here is to find the right combination of e-cigs and e-juice that works for you, and without going broke in the process.