Personally, I use a 2 pass VBR for most of the files I export as mp4. I create, and save, a custom setting so I will be able to use it again and again. I have a T4i and have used the custom settings for exporting clips to the mp4 format.
You might find these links useful:
http://forums.creativecow.net/thread/24/893298 - look at the post from John R.
http://forums.creativecow.net/thread/3/939378
From the second link above and the explanation by Walter S. which one you should use will depend on the length of the clip. CBR would be fine for short clips but 2 pass VBR would be better for longer clips. I hope this helps.