In the high voice version of Sacred Classics, published by Hal Leonard, the Bach/Gounod Ave Maria is in the key of F. However, judging from the range, I could see how it could easily be done in G by sopranos as well, as Fiona mentioned. As with most songs, IMO, you should pick a key that works best for you, versus the one everyone else is using (unless it's an aria, but that's another topic entirely!).
Jennifer
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