From the limited experience of Command Ops' demo (still deciding myself), I think the AI is MUCH better and more aggressive. I didn't play COTA that much, but that's only because I found that I could beat the AI senseless in every scenario I tried. I lost horribly in the demo.
Of course, this is partly attributable to the differences in scenarios, so not a definitive fact. However, there are two other factors to consider -
1) Chrome - you can actually click on equipment in Command Ops and get a description of its capabilities, a photo, etc., instead of just getting the generic-feeling TOE alone. Not a big deal for some people, but I really like things like this in a game.
2) Order details - there's a much finer level of control over your forces.
I also think the scenarios in Command Ops can be much larger than in COTA, but perhaps someone could correct me? I think the largest maps in COTA are about 40x40 km, how large are those allegedly huge Market Garden scenarios in the expansion pack?