A user’s profile shows which record types are available to that user when creating or editing an object. One of these record types is marked as default. I’m able to get at that info via sobject describe with the user credentials, and then looking at the recordTypeInfos.
The answer for me was to move to winter ’14. (v29.0)
The page layouts describe REST endpoint as of that SF version returns a boolean as part of the result: “recordTypeSelectorRequired”. If true, then the user should be prompted to choose a record type on create. If false, then the default record type should be used.