Regarding the optical qualities...
I think the 3-9x is pretty good except for tunnel vision on 3x. Set it on 4x and it's good to go. Light transmission, resolution, and glare/flare are really pretty good.
The 20x is dim, but is to be expected with the exit pupil. I no longer own this scope.
The 3-15x is a little disappointing on 15x, but overall it's tough to complain about for the price. I had one for awhile then sold it. I think the SF is a weak point, but haven't heard of any problems.
The 6x and 10x are solid as stated by others. 10x is more of a specialized tool. Several of us ran an informal test and none thought we could get on a mover as fast as we'd like. My 10x scopes are on play rifles, not hunting rigs. The 6x is a breeze in comparison. An 8x would probably split the diff in the right direction.
My only complaint with the fixed Super Birds is glare on the ocular lens. Under certain conditions, it'll affect the image but it's a simple matter to re-position slightly or block the offending light source. The 3-9x does not suffer this. In no way would this keep me from buying more fixed powers. Nothing comes close as they state, even for more money.
