I'm also curious about wich one is recommanded. FWIW, I use a variant of the first version (wich I find shorter):

Guid UserId = new Guid(reader["UserId"].ToString());

>Hopefully somebody can provide a better way of doing this. The UserId field in my datareader is uniqueidentifier type in SQL Server.

>Guid UserId = new Guid(Convert.ToString(reader["UserId"]));

>Would this be better (more efficent):

>Guid UserId  = (Guid) reader["UserId"];

>Overall, is it better to use the System.Convert method or do a cast like the second example?