I used and liked Smokeless Image X2s and their clearomizers (These are essentially eGo type batteries with an 808 thread). Would occassionally get some leakage from the bottom or from a crack from accidental abuse. Then I filled a new clearomizer with a bakery ladies' strawberry-lemonade flavor and within minutes it had totally melted in my hand. That started my quest for pyrex tanks.
In case you weren't aware, there are some e-liquid flavors that can have a chemical reaction with the p
olycarbonate tubes of tanks and clearomizers. These flavors can crack, melt, or otherwise ruin your tanks. There is a list of these flavors in this link that continues to be updated:
http://www.e-cigarette-forum.com/forum/tanks/219179-lets-make-list-juices-flavors-crack-tanks-ce2s-clearos-29.html#post7203876
The above incident was just before I advanced to using mods and cartotanks. I use cartomizer tanks 99% of the time currently. 1% of the time I'm using ce3s just to test sample flavors.
I haven't found anything else that can beat a cartotank's flavor, or the all day convenience of not needing to refill a tank, or the ability to carry 3-7ml of juice in one device.
I use pyrex glass tanks almost exclusively, aside from a few
polypropylene tubed tanks that are also immune to the volatile juices. There are more and more vendors recently coming onto the scene that are offering inexpensive pyrex glass-tubed tanks.
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I've tried the Smoktech Titans, a vivi nova clone. Although I liked the easy fill tops, they lacked the ability to provide the flavor that my cartotanks allow me.
I've been browsing the rebuildable atty (RBA) threads and am encouraged by the positive reports these are getting. I suspect that these may lead the way to the future by becoming the best juice/flavor delivery system. For the time being, they are too expensive and fiddley for the masses.