Unfortunately, I can't compare ADO vs. OO4O. I started to use OO4O as an alternative to ODBC and I've never felt need for ADO.
In my experience, time of making DB connection depends on load of server rather on driver type on client. (I mean dedicated server, not MTS). Since our sessions are days long, time of making connection is not so interesting for us.
I personally appreciate OO4O for its ease of use and some nice features (searching dynasets, connection pooling, autobinding of bind variables).
For VB, OO4O is much better than ODBC but I've never met ADO or Forms.
Ales