GeoAPI or SimpleGeo?
haxplorer: I haven't used both these apis. But from what I see, GeoAPI seems to provide writable layers if you would want to augment their data with your own data which would be available just to you, while simplegeo doesn't provide it yet. On the other hand, Sinplegeo seems to give an API that enables you to query for predicted population density in an area. Simplegeo seems to provide history for the users or objects that you are tracking while geoapi doesn't seem to provide. See which of these features matter to you and which don't. These are from what I understood by going through the docs in a few mins just for answering this question since geo is one of my interests. So, I may have overlooked something. Please verify these yourself once.