OK... no answer to my question. I'll summarize just by saying that sp_Send_DBMail is support and CDOSYS is no longer supported. That, not withstanding, I almost always use CDOSYS for anything for 2005 and below because CDOSYS will allow you to create your own "From" and sp_Send_DBMail didn't get that feature until 2008. If you need them, there are some features in sp_Send_DBMail that are a little tougher to initially code for, such as the ability to include the result set of a query as an attachment.
So, as with all else with SQL Server, "It Depends". 😉
--Jeff Moden
Change is inevitable... Change for the better is not.