+1 for the Spark SD52. Sadly, I don't use it too often but the key reason I bought it was for combination of output and added runtime, as stated by a couple of the responses. And, although it seems bulky, I don't notice it that much when I'm wearing it on my head.
I have to admit that I tend to reach for my ZL H52Fw first.
I also find 2xAA easier than 3xAAA which is not only costlier but you always have one spare battery that you have leftover. Also, for headlamps, I have standardized with AA as my primary battery... Along with one 18650 headlamp since I have also tried to standardize with 18650s for my hand-carried lights.
I sort of feel the same as those who mentioned size and bulk being a contributing factor to using a smaller headlamp and, these days, I can't believe that my first headlamp was a Petzl Zoom with those big lithium batteries and my second was a PrincetonTec Apex that was 4xAA. We have come so far since those days!
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