I think it depends on your running style to some extent. Do you bounce?
I'm not allowed to spend much on running stuff, so I've just got a 'normal' cheap SportsDirect Slazenger; this one I think (or very similar):
I'm running 4 miles to/from Reading station 3 times a week, with a laptop, phones, and various items of clothing in it, and it's fine. That's at sub-7 min mile pace, but I do have quite a 'flat' heel-striker action. The bag does have a little cross-strap between the shoulder straps, although I don't always remember to do it up, and don't notice the difference when I don't.
Never tried running with a 'proper' runners' backpack.