Either one works well, assuming a scope with a low power of 1X for shooting with both eyes open. (No more than 1.5X, and even 1.5 will strain the eyes if used for an extended period of shooting with both eyes open.) Scopes are bulkier, but have the advantage of turning up the power to 4 or 5 for more precise shooting. It really depends on what you want to do with it. For pure speed I seem to be a little better with a good dot.
A red dot at 100 yards would not be my first choice, but that's just me. I think 50 yards is pushing it with a red dot, and I feel more comfortable with it inside 25 yards. I have a 1.5-4.5x20 scope with a red dot on a 45-degree mount, and I think the scope is fine at 1.5x down to 25 yards. The scope doesn't have an illuminated reticle so under some low light conditions the red dot might come into play beyond my personal limit of 25 yards. This is just my opinion, and you know what they say about those. (Beside it being worth every penny you paid for it.)
I didn't think much of red dot stuff until I tried an Eotech. Now I want to buy another one. That super fine 1MOA dot is just right for my eyes. If Aimpoint ever makes a 1moa dot then may the best man win.
I like the quickness of a red dot, but I can't quite handle it the same as a floating illuminated reticle. Those are the quickest for me. Or the reticle with a 6MOA circle around it. The dot just isn't enough in front of my eye when I'm looking at the target.
I've shot consistently with an m4a1 with a 2moa aimpoint at 300 meters. I actually shoot better with a red dot than with a scope. I think a scope, especially above 8x magnification I overthink and over-analyze my shots. With a red dot it's plug and play, I accept non-pinpoint accuracy, but am often more than happy with my accuracy.
I run a 2moa SPARC on my AR, I can consistently put controlled pairs in an A zone of a USPSA target out to 150 meters.
I have good eyes, ~20/15 or better in both eyes, for me considering accuracy and speed the red dot is king to 250 meters hands down.
For me it can go either way. I actually prefer an ACOG for more precise shooting but that wasnt an option. I can shoot as well with a red dot or an illuminated reticle. Although the new EOTech Zombie Stopper Holographic sight looks pretty cool with the Bio-hazard symbol illuminated with the dot in the center.
Check it out.... Product: XPS2 Zombie Stopper | L-3 EOTech Holographic Weapons Systems
Based on an article I just read in Outdoor Life, it seems like the dot would be better than the reticle -- especially in low-light situations. They stated that the lighted reticle is more a gimmick than anything to sell scopes. And especially in those low light situations, superior glass will give better results than lighted optics any day of the week. In fact, they say that the lighted reticle may actually make it more difficult for you to make a shot in low light.......
Those photos are of the actual reticle I'm talking about and are blurry only because it is hard to take a photo of something like that.
In my limited experience, I need a red cross hair or circle-dot reticle. A single red dot is hard for me to use and find in daylight. Even if the dot is bright, it just takes my eye too long to find. A larger, but still fairly fine, reticle allows my eye to pick it up quicker instead of hunting for it. I'm not talking shooting from a rest here, although I still prefer a red reticle from a rest.
Concerning low light or night shooting, these red dots can be turned down to eliminate red glare and work well for me.
Of course, Outdoor Life is about hunting and hunting distances may be far enough away that a red dot or red reticle just isn't fine enough or have the magnification needed.