I generally use rechargeable NiMH batteries (Eneloop/Eneloop Pro/Ikea Ladda White) for most applications nowadays.
But for non rechargeable batteries:
AlkalinesI've not been a fan of using alkalines for about the past 10 years or so.
The biggest worry is that they will leak inside your equipment.
Duracell around the time of being owned by Proctor and Gamble started leaking, and have ruined a bit of kit. They did have a "Duracell Leak Guarantee" warranty and would replace the batteries, and potentially any ruined equipment but I'm not sure if they still do that now.
Leaking isn't confined to Duracell though, I've have various brands of alkalines leak - all well within their expiry dates. The most recent was the free alkalines (that came with an aldi torch). This leaked inside a cheap torch I had but luckily I checked it and was able to clean the negative contacts before it the corrosive material ate through the rubber seal.
So I don't recommend alkalines these days, especially if you happen to leave the battery inside equipment for a period of non-use. If you do choose alkaline, make sure there is some form of guarantee to repair or replace damaged equipment - eg
http://www.energizer.com/about-batterie ... ry-leakage.
Lithium Primary (non-rechargeable) These are the longest lasting AA option with very long shelf lives. They also happen to be the lightest and the battery chemistry is not prone to leakage like the alkaline versions. But they are expensive in comparison with Alkalines.
They also have a flatter discharge curve compared with alkalines, meaning that if your torch does not have a regulated driver, using lithium primary batteries, it will maintain a constant brightness longer than the alkaline battery. Torches with direct drive and alkaline battery will become dimmer with use, while using a lithium battery it stays at a more constant level of brightness, before dropping off sharply when the battery is depleted.
I use Energizer Ultimate Lithium primary batteries for some applications where I require the the full 1.5V from an AA, or where I am trying to save weight for through walks, eg my Steripen Classic (lasts longer than using rechargeable NiMH even Eneloop Pros), or my Garmin GPS.
They have very long shelf lives - my batch bought in the past few years have expiries of between 2028 and 2036. And they will hold their charge when not being used, as long as there is no draw from your torch.
As mentioned, the downside is that they can be expensive. The cheapest is usually around $15 for a four pack.
I have the Olight S15R (the rechargeable version of the S15). I use a mixture of 14500 and NiMH batteries in it, and on occasion have used a lithium primary battery in it. The lithium primary gives around about half the brightness in full mode compared with the 3.7V 14500, but I found it can last longer than the 14500 in terms of usage time.
If you intend to leave the torch unused for a period of time, I usually recommend removing the battery, but with my Olight S15R, if you twist the tail cap a quarter of a turn loose, it acts as lockout mode. This can make sure there is not a vampiric draw from the torch while you leave it unused with a battery inside.