If a separate emergency kit with a light is maintained then Lithium CR123 is a better choice. Lights using CR123 can be smaller and lighter than AA lights. But the big factor is performance: a CR123 light will still have 80% of capacity after 10 years, and a CR123 self-discharges far slower than Alkaline AA batteries in heat and retains much higher capacity in cold environments. A CR123 light will also generally be brighter than an Alkaline AA since a CR123 supplies twice the voltage and much more power than an Alkaline AA.

I recommend that any dedicated emergency flashlight use CR123 batteries in order to be sure it will work (and will not have leaked!) when needed, even if your kit is years overdue for inspection & replenishment, even if your kit is stored in an extremely hostile thermal environment such as a car.