3-10 x 40 mm with a 30 mm or 1.2" tube.
I have a Burris LRS 3.5-10 scope with a 30mm tube on my AR that I use for coyote hunting. It has an illuminated dot in the crosshair, and I never gave illumination a thought until I went coyote hunting at night. I couldn't see the crosshair in the dark, but I could see the red dot! I have scopes with more than 10x power, but I have found 10x to be plenty...
The best feature, in my mind, is that the illumination turns itself off after 1 hour. Perfect for absent-minded SOB's like me!