I've got several pair of clipless pedals. The Shimano SPDs are the easiest to get out of. My wife stole my M520s for her road bike and will not let me put anything different on it. She has come close to falling a couple of times but always got her foot out and down.
I have A520s on my commuter and M505s on my MTB (replacing the stolen M520s) and have never gone down with either of these. I have a pair of VP SPDs and they can be an issue geting into and out of. I have Nashbar ARC compatible pedals on my road bike and have gone down with them once. They are a bit tricky to get out of. Once I wear out the 2 pair of cleats I have for them, they will be replaced with Shimano SPD/SLs.
I'd recommend getting a pair of M520s, set them at the lowest release tenson and see if that doesn't solve your problem. There really is a difference between Shimanos and the knockoffs.