I haven't seen/used an mStand, but I've heard that some find it to be a bit too tilted. The Griffin is rather ideal (I own an Elevator) and also has the virtue of being cheaper.
On my MB, the screen can sit 90 degs and about 15 more beyond that. So if your desk is really low or you ar really tall, I guess it's bad. But that can bee easily fixed by putting sumthin' under it.
I like the mStand best, the Griffen elevator has this big ugly Griffin logo on it which bothers me a lot. If it doesn't bother you then I say go for the elevator since they peform the same function but the Griffen version is cheaper.