Having used real life battle rifles (as I'm sure at least a few of you have) I prefer non-magnifying optics. A red dot is awesome for quick acquisition. Iron sights are nice if you can spare a second or two.
Running an optic on a carry handle is a pain; not pretty, and not comfortable.
I guess speaking from experience, the first shot is usually fired before you are actually 'on target.' If that's the case, why not get the quickest possible eye on target?