Generally both are equally well understood.
However, you should think "parallel." What's good for the goose is good for the gander. If you follow one with a construction of any sort, then the other should have the same grace.
Therefore it would be "either AT our office or AT your office"
or AT either our office or your office."
To say it the other way, "either AT our office or your office" leaves an unbalanced AT in there. And we certainly don't want unbalanced ATs now, do we!
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