There probably won't be one agreed answer on this one.
The G2 is still new, so not as much experience. I find the 200-500 to be better than the G1...as long as the 500-600mm focal range wasn't needed. Fixed aperture, more light, faster AF. Can't comment on the G2, but I suspect it'll still be slower than the 200-500 due to variable aperture.
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