I have 4 ACOGs. I just love them. No scope comes even close in the combo of compactness, glass quality, and Field of View (FOV). 4x ACOGs have a FOV as big as Magnified optics with 56mm objectives! Only negative anyone can say about ACOGs is the short eye relief, however, if you are using a AR15 type that shoots .223, this is not really an issue for ex Military guys because we were taught to shoot NTCH (nose to charging handle) with Irons. As long as you shoot NTCH with ACOGs, you will always have the proper sight picture.
If I had to nitpick, I would chose TA-11 Series (3.5x) over all others as my favorite. TA-11x eye relief is 1" more than 4x ACOGs (TA31x, TA01x), but it feels like it is much more. 3.5x ACOGs are great for .308s as the extra eye relief is needed for the extra recoil. Only negative of the TA-11 is the heavier weight and the slightly smaller eye relief.
My favorite reticle is that of the TA-01NSN. It is the easiest to use and is most accurate,. however TA01NSN does not have BAC. BAC is a very usable for CQB, and with a front scope cover, is almost as good as a red dot.
I do NOT like the TA-33 ACOGs. FOV is half of that of the 4x ACOGs, it is like you are getting half the picture for almost the same price. Also it sits way too high (with the stock mounts).
To me there is no real difference with the TA31F and TA01RCO, both reticles are basically the same. However, the RCO does have safety wire so you can't lose the caps, and it offers no tools adjustment. Which does not seem like much for the price difference, but it is very nice to have. RCO also comes with a cool looking kill flash.
My 4 ACOGs, Top to Bottom
1) TA11F on AR10 16" Rainer SuperMatch Barrel
2) TA01NSN on LWRC M6A2
3) TA31RCOM4 on Noveske N4-Light
4) TA31F on Walther/Umarex/Colt .22LR