Hey GShelly, it really depends a bit on your
vaping style and what wattages you want to run your new mod at. I am not the greatest at battery lingo, but you want something most effective for your vaping "style". I am a MTL vaper so for me a battery with higher mAh (meaning longer runtime at lower wattages or higher amps, is it? Sorry it's a bleary new years day for me a bit.
But basically if you want higher run time at lower wattages you would select one type of battery vs. if you vape very high wattage, you may have to sacrifice some mAh in order to reach the wattages you want to have in your vape. I'm sorry I really suck at explaining this, but I'm sure someone will be along to fix any errrorz.
Mooch is a much better explainer of these things and also has a list of approved batteries on his BLOG which I am very bad at inserting the table, but it will give you a list of "approved" batteries and vendors as well as an explanation of each and what they are useful for... Do'h seems like I managed it this time, but you can also check out his blog for more information...
Best of luck