I have both the Gerber IU and several Fenix products. As stated by others, it depends on what you want it to do. The Gerber will be tougher, and can be easily clipped to a ball cap to double as a headlamp, but isn't as bright, but will go for 35-40 hours. If you want something more powerful, you may want to go with the Fenix L1D CE. The Fenix P1D CE is the 1 CR123 light, not the P2D CE as stated above. The P1D CE is my EDC light, as it is tiny, the twist mechanism is reliable, and it's bright.

AA's should be far easier to find locally, so if you are there for a long time, that should be your choice. If I were going and had one choice, it'd be a headlamp, hands free is a huge benefit. If limited to those 2 options, Gerber. If you want a do it all light and money isn't an issue, look at a Novatac.