Depends what type of vaper you are.
Start by doing some research, here's a good place to begin Choosing a rebuildable tank (RTA) from the MANY choices? | .................. Forums - An Ecig and Vaping Forum
and
Help choosing an RTA that doesn't suck. | E-Cigarette Forum
I've been using a subtank mini(version 1.xx not the new aqueous coated ones) for a few months, had to do work on it for the rba to be adequate. Enlarged both the liquid feed and air intake for a proper lung inhale. The premade coils work well, and the new vertical ones are even better as is the new rba section.
Thanks for the links, I will go research!