It's really hard to give a firm answer to the question of what the "best" battery would be. They all have their advantages and drawbacks.
Here are the pros and cons of the
batteries we carry,
Ultrafire 18650 XSL:
Pros:
Low-priced, hold up fairly well, and last a long time between charges.
Cons:
These are not high drain, the hit does drop off as the battery discharges.
AW 18650 3100 mAh:
These
batteries are renowned for a very high quality build.
Pros:
Lots of mAh (longer lasting), very high quality, high drain/discharge so they do deliver a consistent hit.
Cons:
Price (though, even with the higher price, I don't think I've ever heard someone say they regret getting them)
AW IMR 1600 mAh:
Pros:
High Drain/Discharge so they deliver a consistent hit, more cost-effective than the 3100
Cons:
Lasts about half as long as the 3100 mAh battery.
Ultimately, it's tough to answer the question of which is "best" because it really depends a lot on what you need out of a battery and how much you want to actually spend. Hopefully, this list can help you make a decision more easily.