Lithium Energizer AA and AAA cells are the best. They are lightweight, work down to -40 degrees Celsius (Alkaline Cells begin to fail around 0 degrees Celsius) and have a higher energy capacity than the best Alkaline Cells together with a longer shelf life. In high drain devices the differences between Lithium and Alkaline cells are even greater. An example would be for a flashlight (Fenix L2T) shown below



At a lower current drain the differences are less marked,



The downside is than Lithium Cells are considerably more expensive. Typically a good Alkaline (Duracell) would be around $0.40 compared to the Energizer Lithium at $2.00 each.

I would recommend the current high performance NiMH Eneloop cells from Sanyo with a good quality charger (own brand Sanyo would be decent enough). The Sanyo Eneloop cells keep their charge much longer than ordinary NiMh cells. A portable solar panel and battery charger would be useful also as a backup.

So if the application for your batteries is absolutely crucial and has to work in a wide variety of temperatures and the requirement for a very long shelf life then the Energizer Lithium AA and AAA cells cannot be bettered. For all other requirements then the Sanyo Eneloops will be better than standard Alkaline Cells as they can be recharged up to 1000 times and will be much more economic over the long term and much more environmentally friendly also.