For any magnified scope, having it mounted on a flattop upper is VASTLY superior.  For any conventional scope (unless it is super-large), you won't find any better mount than the Armalite one-piece mount.

Here's why:

www.ar15.com/forums/topic.html?b=3&f=12&t=101429

On the other hand, if you're using a dot/reflex type sight, the best setup is a forward-mount "gooseneck" on a carry-handle upper, as your irons are still there (permanently) and instantly usable, and the forward-mounted dot sight gives you speed and the ability to aim without a cheek weld.  It is also cheaper and more reliable than buying bolt-on "back-up" sights.

-Troy

For most optics a flat top uppper is the way to go.  If you use Badger Ordnance Ultra High Rings you eliminate the need for a riser to get a good cheek weld also there is no intermediate part (the riser) and that eliminates the possibility of an additional part that can affect the stability of the scope mount and therefore accuracy of your shots.



You can learn more about Badger Ordnance Ultra High Rings at the link below:
www.glocksbr.com/axami/shop.php?grd=35

Denny