I run a lot of Cover 3 vs the CPU on All Madden, and most of my success has been playing the curl-flats. I lay off enough to discourage the deep corner, but am ready to instantly bolt toward the flat. It works pretty well, as I am often able to bait the QB into throwing short and then run up and make the tackle, but I often miss passes more in the middle of the field.
That or I play weakside defensive end and pass rush.
Anyway, you've got to make sure your defense is in position to defend the run, because they will toast you on All Madden. For example, if I'm playing the curl flat in cover 3 and they line up with 3 WRs to my side, I WON'T line up over the slot WR. Instead, I'll play near the line and then run that way at the snap, so that I'm in position to help with the run.
EDIT- oh yeah, I should also mention I play in the defensive camera mode exclusively.