As far as raw strength with the Light goes, Ana. Shin has the fastest hand of the Gunslingers, but that doesn't mean his GG is super powerful (even a Hunter fresh out of the grave can immediately disintegrate people with GG).
Ana on the other hand, had a GG so strong and bright that its impact spots continued to burn long after they hit their mark. No other hunter has shown a feat of that caliber.
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Dude. Shin Malphur FORGED THE GOLDEN GUN.
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And? That doesn't mean he's the strongest; if anything, it makes him the most lethal Gunslinger because he can't be outdrawn. Ana's is the strongest Hunter we know of because her Golden Gun was known to create a flaming crater in their impact zones. It would be like comparing six shooter GG to bottom tree GG with celestial nighthawk; there is a clear difference in power.