Greetings!
This was a very difficult poll for me to vote on... I was very torn between CR123 and AA, the only two cell types that I buy lights for.
I finally voted CR123, because that's what my Surefires and most of my Inovas use. However, if I lived in a perfect world where any lights could be purchased with my choice of batteries though, I'd probably go with AA since they are so amazingly easy to obtain, inexpensive, and available in so many great varieties. Also, most of the benefits to be gained by CR123 Lithium cells can ALSO be had in AA form by using Energizer Lithium AA cells.
Best wishes,
Bawko