santiago's been a decent defender at SS, at least over the past 4 years (with the exception of last year, but doing better this year). the way everett has been regressing over the past 4 years shows he's likely to do the same. my guess is over the course of this season, they'd be equal, but that's just judging based off uzr.
so play him vs. rh, guillen for the occasional lh starts.