If you're sub-ohming, VTC5 is known to be the best but it's kinda hard to find them, at least the non-fake, legit ones. VTC4 and VTC3 are all good, all with 30 Amp limit but again, you need to watch out for fake ones. Samsung INR 25R and LG HE2 are also really popular for the similar quality and stability and they are easier to find, but I think they have less amp limit, probably around 20A to 25A. However, it doesn't really matter if you build your coil above 0.3 ohm (but make sure you have an accurate ohm-meter) as long as the battery's amp limit is above 20A. I don't recommend buying Efest or any batteries with 'fire' in the product name, just to be safe. Why? Batteries can turn out to be a venting mess or in the worst case scenario, a bomb, even from a reputable maker, so why risk it from less known companies? That's my logic, but many people are enjoying their mech mods with those batteries so I don't know.