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If you want to use lithiums, 123's are more cost effective. The idea of an AA light is to use readily available alkaline AA's. With lithium AA's, just one set in the flashlight and one spare set will end up costing more than the flashlight itself does.
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If cost is the primary factor then, yes, it would be more cost effective to use high output flashlights that take 123 cells instead of lithium AAs. For me though, cost is not the primary consideration, my primary consideration is minimizing the amount of weight I have to carry in my pack thus I like to have my lights run on AA cells as does my GPS and radio so that I can minimize the number and weight of spares that I have to carry.