i have an mbp, i love it. it's still really powerful, and i do quite a bit of processor intensive stuff; i've never had any problems.
it really comes down to whether you'll ever need it to be mobile. the mbp is really useful if you go on trips and need to dump footage/edit on the go, but if you're going to be staying in one spot then obviously the imac is the way to go. both will be solid for video editing.
if you go with the mbp, be prepared to drop a lot on external hard drives for both storing as well as backing up.
The joy I get from skiing...that's worth dying for. - CR Johnson