In terms of service, Cathay Pacific is possibly the best among the three airlines that you select.

In terms of economy class, TG and OZ actually offers better legroom on its Boeing 747s and 777s and long haul fleet, which is around 34 inches (CX is only 32")... But there is no personal TV on TG Y and most of OZ fleet (except Boeing 777s). Meals wise -- TG actually offers the best meals among these three airlines.

In terms of Premium class service, CX is definitely the top of the notch, and TG has the weakest product, although the new A340s that TG will receive next year may feature a better F and J product. For now, TG seats are very outdated, especially on the older Boeing 747s and 777-200s. OZ is slightly better -- J cabin is okay and F is only offered on Boeing 747-400s, which offer a full flat seat. I think both OZ and TG offer very aggressive discount on its premium class. In terms of meals, Asiana offers more variety than TG, but OZ offers no amenity kit in J (But TG has amenity kit in J). Both airlines have F amenity kits, but no pajamas.

In terms of customer service, CX scores the best, with OZ on a close second, and TG the last.

I hope this little guide will help.