I have low powered variables from Weaver, Nikon, and Leupold, myself, and have mounted Bushnell scopes for others.
The brightest is, believe it or not, the Weaver 1X-3X. It also has a FOV that you can literally shoot clay birds with. Right behind that is the Nikon 1X-4X and the Leupold 1X-4X. The Bushnell 1.5-4.5 X 32 looked OK, by I can't vouch for how it will hold up, or the adjustments. It's very reasonable for price.
On a slug gun, I suspect the Weaver might not last forever. I have them on a .35 Remington, and a 77/44, and they are great there, but they are also pretty mild kickers. If the Weaver dies, it seems the customer service is lacking. The Leupold will absolutely hold up, but costs a bit more. The Nikon has seen a lot of 3" magnum use, and has not missed a beat.
For low light use, you want the best scope you're willing to pay for. You want a bold, or illuminated, reticle. The bigger the objective lens, the better. Then experiment with the magnification to figure out what power will let you see in the least light.
My shotguns are used for hunting so I have red dot sights 1x on all of them. great field of view and very accurate. Cross hairs are not much good from 10 minutes after sundown till closing hour. red dot is perfect and has a SUPER wide field of view for deer/bear/turkeys.
You did not mention a price range, but up to it's price I've seen nothing to compare with the Leupold VX-R in either 1.25-4 or 2-7 size with their firedot reticles. I own low power scopes by Burris, Bushnell Elite, Leupold, Minox, Nikon, Pentax, Redfield, Weaver & Zeiss. None can come close to the low light performance the VX-R provides with it's illuminated reticle and quality glass.
The best, as Tnhunter said, would be a Leupold VXR w/ FireDot. But they are upwards of $600. A decent one that I've used is a Mueller Multishot 2-7x. I put one one a rifle I converted to .356 Win., it was $145. They have a smaller one, the Speedshot, which is a 1-4x, but I like the reticle better on their 2-7x.
Taking this discussion to a slightly different place, I'm looking at low-mag scopes for my Marlin 336 lever action, and have narrowed it down to Weaver's 1-3x, or one of Leupold's 1-4x scopes. Looking at the Leupold, their VX1 Muzzleloader/Shotgun model is everything-proof, about 9 oz, 9", 92% light transmission, full warranty - for $200. Their 1-4x Hog scope is - as far as I can tell - basically the same thing, but $30 more. Their 1x4 VX2 is, again, basically the same thing - as far as I can tell - but $100 more.
I can't see one iota of significant difference among those 3 scopes, and so cannot figure out why I shouldn't just go with the $200 model. Am I missing something, other than the chance to give Leupold more money?
VX2 gets you better lens coatings than the VX1. The hog scope is a VX1.
I had an older version of the 1-4x20 Muzzleloader/Shotgun model on a rifle for quite a while. I like the heavy duplex. That rifle now has a 2-8X32 on it. The bigger objective is a lot better in poor light.
The answer to that question will really depend on the kind of shooting that you will be doing and the kind of gun that you will be shooting with. Visit the best rifle scope guide to find a one of a kind comparison chart that will give you detailed rifle scope reviews of the most popular rifle scopes.
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