Why?
"Best" is a term that I never understand why people on forums have to obsess with. Far too subjective and totally meaningless without context.
Personally I've found most AA lights a little underwhelming. Poor performance and poor runtime most of the time.
The "best" light I have that uses an AA sized battery (a 14500) is the BLF Kronos X5. It's not especially compact for an AA sized light, but significantly smaller than a comparable 18650 light. And it's output and throw are simply out of this world for such a compact light.
Superb tint with the NW XP-L HI emitter. And super usable 7 output programmable driver. With Moonlight and a good choice of low modes that you can actually get pretty good runtimes and lengthy EDC carry with it.
In terms of compact dimensions. I really like the the ThruNite T10 (think it was also called Sabre 1A). It tail stands, is very short an narrow. Has 4 good output modes including an ultra low moonlight mode. And the beam profile with an XP-G2 is very very good, as is the output considering it runs on a 1.2v Eneloop.
But sadly the threads are super noisy, the head is lose fitting with lots of slop and the tint is completely ice white.
I don't have a pic on it's own. But it's the 3rd one in from the left. Note it's shorter than some AAA lights.
What I think would be a nice AA light, is if Maglite made an AA Solitaire with two or three output modes. The head tight for off is so much better than head lose for off design.