I'd think the mAh is the best to decide by if you need longer time
Yes, for flashlights. For advanced personal vaporizers (mods), NO! For mods, we need to be using safe-chemistry batteries. In some applications, the amp rating is more important than the mAh rating.
As stated previously by those who know their batteries, the batteries with the higher mAh ratings are protected ICR Li-Ion batteries. These are no longer recommended to be used in mods. Due to their voltatile chemistry, they can be dangerous should they become stressed or shorted in a mod, which can lead to venting extremely hot gas, flames, and possibly explode. These batteries often have inadequate amperage to power many of our high drain mods safely.



High-drain safe-chemistry batteries are relatively new on the market. These are called "IMR", Li-Mn or unprotected batteries. Their safer chemistry may still vent gas if shorted, but with a greatly reduced chance of flames or threat of explosion. These batteries excel in regulated variable voltage mods, mechanical mods using a Kick, or any mod using a rebuildable atomizer because of higher amperage capability.
Also stated, do not use any battery with "fire" in the name: Surefire, Trustfire, Ultrafire, or whatever. These are low quality batteries whose advertised battery specifications are wildly overstated. They might be safe to use in flashlights or other low drain appliances, but are not suited for mods.
For a large list of these safe-chemistry, high-drain IMR batteries use this link:
Battery Basics for Mods: IMR or Protected ICR?
More information on batteries & chargers here:
http://www.e-cigarette-forum.com/forum/batteries-chargers/546143-batteries-chargers-multi-meters-forum.html