Below is what I use, anyway. The first two from the left are BUD cartos filled with homemade supermelts w/ 30% EJMix. The next two are the shorter pre-filled O-Pen-Vape 1/2 gram BUD carts from a local dispensary. The 5th with the rounded driptip is a single coil Mini Protank 2 with 1/2 g of PureGold. It's what I like best for PureGold. The PureGold seems lost in the vastness, but it slowly pools into place and feeds fine with dry pulls. I can always get a couple medicating hits without giving it the slightest thought or preparation.
The 6th is a Mini ProTank 3 that I like best for the VG e-liquids I mix. The ProTank 3 uses a dual coil and for many reasons I prefer it (only) for e-liquids.
The Kangertechs use replaceable heads, the BUDs are disposable. The BUDs have small tanks and it's a breeze adding or removing liquids. 99% recovery is easy with an 18G needle. The commercial O-Pen-Vape liquids themselves can be mediocre, but their carts have all the pros and cons of BUDs.
Kangertechs work without much fiddling but in case of trouble it's harder to recover all the goods. The BUDs require dry pulls and frequent burping for best taste etc, but the end result is very good, so I'm fine with that. If used in "it should just work" mode the dry burned hits will disappoint. As soon as the taste gets a bit dry, pull the cap and the blue plug for a moment.
Not perfect, but all these are very usable. With 2 ohm coils, I set the voltage to 3.3 - 3.5 volts. All the liquid then simmers unburned and the vapor tastes good, though in truth no hot oil is great on the throat. A longer cooling pathway or water would help, but isn't too practical. More power, lower resistance, creates more vapor faster, but some of it burns where the wire glows, which reduces health benefits.
I usually carry the carts separate from the battery, on their side or upside down. I've never lost more than a micro-smear of any liquid, except for that gorgeous thick clear golden EJMix & Sour Diesel liquid on the left (Oh, my heart aches!) that I tossed, kit and caboodle, when approaching a border.
The little caps on the BUD 510 connectors are great. Leaking is due to
inescapable physics, wear/hardening of the wicks, or occasional DOA defects - it's a complex subject. It's not that some designs will
never leak.
@sethhobrin, you can get a Mini ProTank2 on e-bay ($10 shipped) and a couple Sapphire BUDs. Then gradually experiment. Mini Protank3s also go for $10. The eGo C-Twist is a good battery.