I have owned many different ACOGs (TA31Fs, TA33, 648). All of them have a purpose. The 648 has the nicest field of view and the ability to adjust the fibre optic exposure was very nice. But it's a beast, expensive and very hard to find.
The TA31 line are nice and have a decent field of view. Of all the ACOGs (or any optic for that matter), the 31 has the worst eye relief. This can be an issue depending on your setup. Running an A1 or A2 stock and a BUIS make using the 31 troublesome.
The TA33 is really a jack of all trades. It has amazing eye relief. The specs are way off on the box. The eye relief and box are simply amazing. I have run my TA33 sideways, upside down, under obstacles, and using the BAC, it's just like a red dot. I never lose sight of the chevron. Compared to the TA31, it has better eye relief, but less magnification and less field of view but is also lighter.
I would conclude that if you are "running and gunning", learn to master the BAC, and you would be better served with the TA33. If you will be more stationary, or haven't mastered the BAC, the TA31's bigger field of view with suit you better. Glass on all ACOGs is amazing. You need to also consider the reticle. I have owned donuts, cross hairs, chevrons in red, green and amber. My personal preference is the chevron. The top is a very precise point for accurate shots. For closer up work, the chevron is very quick to paint the target. As for colour, green is head and shoulders above red. And red is far better than amber.
I didn't mention the TA11. For me, it was too heavy. It has amazing field of view, and better eye relief than the 31, but not as good as the 33. It's magnification was also middle of the road. In the end, weight and eye relief was most important to my type of shooting.