I have the Holosuns and the Sigs in green and red dot, both open and enclosed emitter... after shooting all of them on various platforms including a bunch of Sigs, the Hellcat line and all the Glocks, I have narrowed down my Personal preferences to Enclosed Emitter / Green / variable reticle... I feel like green is slightly more bettererer and with a variable reticle you can switch between dot and circle or circle + dot. The only thing I can really think of to say other than my personal experience and preference stated above, is that if you are shooting at any distance, say 25/50 yards etc and you have circle or circle/dot selected and you are shooting at typical silhouette size targets, the circle itself can appear to occlude the entire target, at 25 yards the circle itself is larger than a head for instance, so I find myself switching back to dot for ranges over 25... this is just personal opinion and could be due to being half blind...