The tank of a Carto/Tank setup is very important. A crappy tank can ruin a carto vape pretty quickly!!! A good seal around the carto, tight fitting end caps, and durability mark a great carto tank from a POS tank. A bad seal can flood a carto. Loose O-rings can leat to accidents and spills.
I own 3 IBTanked tanks....the best buy for the most quality out there.
I own 2 Vaporev tanks
Black Rev Tank - Accessories Great quality, but they are only available in 1 size (diameter) and 2 glass types. They are a little more pricy than the IBTs
I also own 2 of the cheap Smoketek Pyrex tanks, they work, but they fit my cartos kind of loose, so spills can occur if you are not careful.
I have a 4 or 5 others which I don't have links to, which are hand blown and look cool, but are a fit funky. I bought them at Vape meets and vape shops.