I listened to what Mr Tude had to say and love IBtanked. They are nice people, easy to work with and sell a super product at an extremely reasonable price (plus they send it in a holder called a thingie which works great). Also really like Loki. They are about double the price of IBTanked, but it is also double the SS in thickness on the caps. That is just a user preference. But for the best quality with cheapest price, haven't seen anything that beat IBTanked. They have 3 size diameters and 2 size lengths to choose from. So make sure your carto size matches what tank you buy. I like the XL tanks, so buy XL cartos. Boge and Smoktech are all the cartos I have tried for now, but plan on trying all I can.
Sorry, just FYI this is assuming you were wanting a carto/tank setup.