If you have a choice between a Zeiss and a Barska, pick the Zeiss.
If you're choosing between two similar scopes, with different sized objective lenses, in low light when your pupil is dilated, you want the bigger objective.
Adjust the magnification so the exit pupil of the scope is about the same size as the entrance pupil of your eye. The bigger objective will get more (brighter, more densely focused) light to your eye.