Have you done your homework with Mech's? With Mech's you build to the combination of Mod, Battery and Atty. There is no real "best', too many variables.
If you're thinking of going into Mech's you need to know this -
1. You must know Ohm's law,
http://www.steam-engine.org/ makes it easy and there's even an app on it for Android
2. Batteries!, Take good care of your batteries and know them!!!!!!!!
a. Avoid garbage batteries like eFest who rewrap with grossly inflated amp ratings. Stick with authentic LG, Sony or Samsung from reputable (not ebay or amazon) sources, great places to get authentic are from
http://liionwholesale.com/
https://www.imrbatteries.com/
b. Stick well within Continuous Discharge Rate (CDR) Not the "pulse"
c. Keep up to date with what Mooch tests and battery ratings, follow his posts on Facebook and his Blog
d. In Mod's with multiple batteries, marry them.
e. Get some battery wraps, they're cheap and easy to re-wrap batteries. Any nicks,tears or what ever don't be stupid and just re-wrap.
3. Don't build stupid low a good builder can chuck and get awesome dense vape from a good build. It's simple, with 20 CDR Amp batteries -
a. Single battery mod's you're fine with .2 ohms on up
b. Dual Parallel you're fine with .15 on up. Parallel take the full CDR of one battery and you can add 1/2 the amp rating of the next battery
c. Series you double the voltage but you share the amp. So a series you build high with a lot of wire, no lower that .4 ohms.
4. Make sure you don't have any shorts. For an extra caution any new build I vape on a regulated mod for a few drips or with a tank about a 1/4 tank. This is to insure nothing wonky with my build or any shorts.
5. Careful if it's not in your hand, if it doesn't have a lock on the button and you pit it in your pocket (which I really don't recommend) insure nothing else is in your pocket and it's loose. Don't want to put it in your front jeans pocket and blow your Johnson off ya know
6. Last but certainly NOT the least, keep it clean! Clean it when you first get it "before" you even use it and clean it on a regular basis.
a. Ultrasonics are a very good investment, got mine off Amazon for around $25.