I've tried:
Vortex PST 1-4x ... small, light, but reticle too small for me.
Spitfire 3x ... reticle too small.
Elcan 1x/4x the best glass of the bunch good reticle ... but thought it cost too much ... no diopter but not fuzzy at 500yds for me.
ACOG 3.5x chevon 5.56 ... the reticle was good out to 400yds but for some reason not at 500yds. No diopter, fuzzy for me.
Burris AR 536 ... fixed power 5x ... like option for lower power 5x too much for low power setting.
Now on my day carbine I use holosun P515 dot site with an EOTECH 3x magnifier behind it. Great dot and great magnifier. And so this setup is a 1x/3x and that works for me out to 400yds. And I like the 1x for under 100yds let's me really see with peripheral vision, both eyes open. I returned the EOTECH dot for the factory refund as the dot was getting fuzzier and fuzzier. I did have it out in an ice storm once. But I kept the magnifier, nothing wrong with it. The holoson dot is good. Not as good as the Vortex 1-6x g2 or the ELCAN, but as good or better than anything else I've tried.
I really like the 1-6x Vortex Razor gen2, great glass, great dot, decent reticle, but that is too much scope for short distance and not quite enough for intermediate (out to 600-700yds) so I use the Burris xtr2 1.5-8x CB Mil for the intermediate space. The Vortex is a close second, with better glass. One interesting feature of the Burris is the reticle is FFP while the circle dot is SFP. So they call it DFP (Dual Focal Plane).