As a private individual vaper I know there is no way I'll ever be able match the collective knowledge of all the expert vapers out there which is why I do my research and see what they recommend as being the best thing to do the job. I have 2 sets of 6 x 18650's that I use in my mods, both of which I researched first. One of my sets are Panasonic NCR18650B 3,400mAh 3.7V and the other set are Samsung INR18650-30Q 3,000mAh 3.7V.
I've had them for 2 or 3 years and never had a problem with them.
Don't go by the brand name though. Every brand sells some high end products and some lower quality versions of the same thing. Not all batteries are safe for vaping. The type of vaping device you are using is also relevent in deciding which batteries will suit your device best.
I like to sub-ohm between 0.15 - 0.3 ohm resistance at around 70 - 90 watts and I use 3 x 18650's in my mods which I feel spreads the load for using high amp discharge rates. Remember, you're putting the thing in your mouth and sucking on it so scrimping on cost and having your batteries blow up in your face is not worth the small saving you might make looking for cheap alternatives.
I never charge my batteries in the mod and only ever use a decent external charger. Don't try to charge them too fast. Most people recommend 300mA as being a good rate to charge them properly and help them last and stay reliable. And, as others have said, keep your spares batteries in a battery storage box and away from lose metallic things like keys and loose change that could cause them to short and potentially blow up.