Brahma
Obi-Bro Kenobi-X
Woah...I highly recommend everyone watch this vid:OVERWATCH CANCEL TUTORIAL - YouTube
Guy explains most of the good cancels and is very helpful. Vid posted up yesterday.
Roadhog is around the 9min mark.
The Genji cancels seem required, they make a huge difference. Reaper cancels are easy enough learn to get a little edge and S76 is kinda minor but useful.
Reinhardt/Roadhog cancels seem massive too.