Flickr is a Possibility.

Aperture 3 also has automated ability to publish to Yahoo's Flickr site.  The integration of Flickr with A3 seems more robust than with FB.  It appears to me that with Flickr you can use an existing A3 Version, not a version created for Flickr publishing purposes.  Furthermore, it appears that synchronization is possible, whereby modification of the Flickr-published A3 version can be conducted-- whereby changes to the version in A3 are newly-applied to the Flickr-published photo-- Changes like Title edits, Photo Adjustments, etc.

I need to explore adding photos or info from either the Flickr or A3 sides.

Many people routinely use FB (tho some never do).  But it appears that Flickr provides an integration with FB that can provide, in your FB site, links to the Albums/Photos that you have published in Flickr.

Facebook is a Possibility.

Facebook is an obvious possibility.  A3 publishes to FB OK.  Some folks can't or won't use Facebook.  Not sure how well a photo's Location information can show up in FB.  It appears that in A3 a new Version, just for FB, is created.  This version, I think, is detached from other versions that have their own metadata, keywords, stars, etc.