They all would work.
The plugin parses the config by finding the first space, then selecting all the text behind it for the message. Next, it takes the letter after that first space for the type. Finally, it takes all of the text after the space behind the type character for the command. So...
!url C say /? url
!url C "say /? url"
!url C say "/? url"
...all do the same exact thing.