As far as the criteria you are listing as important to you, the ACOG is outstanding in all of those areas. Not only will it not shift zero on you; but with a Larue mount, you can dismount the scope and remount it between shots and still have a good group. And as to durability, it is almost literally, bomb-proof. If you search the archives here, you can see ACOGs that stopped 7.62x54R rounds or that were strapped outside of an armored vehicle when a 155mm IED went off.
The TA11 is also excellent in low-light since it has a 10mm exit pupil and excellent glass, so your eyes are always getting the maximum amount of light available. The exit pupil isn't artificially restricting that.
The fiber-optic/tritium combo on the TA11 is also great in that it automatically adjusts the illumination to ambient light. A couple of years ago I started running an Aimpoint T1 in conjunction with my ACOG and one of the things that irritated me is how often I have to adjust brightness on the T1 - not a major thing by any means, but it highlighted for me how spoiled I had gotten from the ACOG. Prior to that I only noticed the auto-illumination when the ambient light wasn't great for my targeting conditions. Running it alongside the T1 helped me realize how often the auto-illumination was just right.
As I've owned the TA11 since 2002, I'll go one and add my two cents to some of the other feedback as well...
Generally speaking, the only shortcoming they typically have is short eye relief.
This is true of the 4x32 ACOGs the military uses. It is not true of the TA11 (3x35) or the TA33 (3x30) ACOGs; both of which are fairly generous with eye relief (in fact, if you shoot nose-to-charging handle, you'll need to mount it at the front of an AR15 receiver to get enough eye relief - though probably not so far forward on the longer LAR-8 receiver).
That said, since they are lit with radioactive tritium, the illumination is going to be 1/2 as bright as new in 12.5 years. Recharging the optic is a factory overhaul job.
This is correct and last time I looked (several years ago) refurbing the tritium was a $250 job. Though since you are going with a TA11, you also have the fiber optic illumination - which actually supplies most of the light in most conditions. The only place you'll notice the dimming of the tritium is in almost absolute darkness where there is no ambient light for the fiber optic to gather. As I said earlier, I've owned my optic for 9 years (and have no idea how much older the tritium charging it might be) and even in absolute darkness, I have a usable reticle (although not much too target in absolute darkness).
And actually, that brings up one of my gripes with the ACOG, compared to Aimpoints/Eotechs, they don't play well with PVS-14s or other night vision devices. The tritium is too bright for those.
but I also get the ability to control the amount of illumination
If you decide the ACOG reticle is too bright from too much ambient light, a strip of tape or an inner tube over the fiber optic lets you adjust the brightness just like you would an Aimpoint.
Overall, I think you will be more than happy with the TA11 ACOG, given the criteria you listed as important to you. However, I would just about bet money that there is probably a more traditional scope out there that is cheaper and that would serve your needs just as well (Trijicon's Accupoint line being a good place to look for that matter). And as much as I like the ACOGs, variable magnification is nice too; but if you want an ACOG, it will certainly do well in the criteria you listed.
