I agree with Kay here. Your question is extemely subjective, based on a thousand different details.
If you're using an eGo, then the answer is much different than if you're sporting a Darwin.
For me, using a Kicked Silver Bullet, the best
tank I've found so far is the GG Penelope. It's a rebuildable atomizer with a tank attached, with liquid control to the wick built in. It holds about 3ml, so I get to top it off all the time. There is a learning curve to using a rebuildable though, one that a lot of people don't care for. I DIY my liquids, so I'm used to the fiddly bits.
One problem with the GG stuff is that it's all hand made by a fellow named Imeo in Greece. He builds a ton of them and then sends them off to various distributors. There's quite a bit of demand though, so most of the devices get snatched up within an hour or two of them hitting the shelves, if they're not all pre-ordered away.