CE4 tanks. Looking now to get a couple more of them for a good price.
If you search ebay for "ce4 clearomizer lot", you'll find plenty of results. You can get 10 for less than $15 including shipping, and if you just want 5 you'd be able to find that for about $8-9. I've bought 650mah Ego clone kits off a guy that come w/ a CE4, and after inquiring w/ the seller, he sells me extra CE4's for $1 a piece. I have had a bad 1 out of 10, but for the price it's not an issue IMO. I personally have 7 in rotation right now w/ different flavors, so they just get light usage, but nonetheless I find them quite reliable for my needs. I just got into the e-cig scene last month, and I've heard that clearomizers have improved a lot recently, even in the past yr. Luckily I never had to deal w/ any crappy stuff, or had to deal w/ any issues when trying to vape. I will say tho I'm kind of a stickler on how strict and careful I am w/ my gear. I ALWAYS keep my clearomizers standing fully upright, as I kno they can be prone to a bit of leaking under certain circumstances. But it's nothing that can't be remedied, or better yet completely prevented. Judging by the sales volume on ebay, I'd say the CE4 type is the most widely produced and used, so the manufacturers have really got these things consistently solid. I have a few CE5's in my bunch of clearomizers which I also use, but I honestly just prefer the CE4. It's nice that the CE5 is rebuildable, but for the sheer low cost of these, it's basically just not worth it to me. I can't justify upgrading yet when I'm still happy w/ this setup, which has been very hassle-free for me thus far.