Its not always about the 18650. Some of us need smaller batteries and I keep forgetting that people get ripped off daily buying these. The EH brand by madvapes are some of the best batteries I have used. For months now they have never given me a problem and they are super super cheap. The nipple tops are a bit more expensive, but I only use the flat top style in my mods. You can stack the 18350's without a problem - I use the in my Vamo and Vmax.
If you own a Vamo - try stacking two of these 18350's - you will see a huge difference.
WHERE:
18350: http://www.madvapes.com/
18500: http://www.madvapes.com/
$3.69 each