Good question with no easy answers. I used Now Health (underwritten by Axa) for many years. They were excellent. Unfortunately due to DHA insurance regulations in Dubai few years back, they have increased their prices, so I searched for alternatives. I moved to Aviva which again was excellent. Unfortunately they decided to pull back from UAE and its customers were taken over by AETNA. AETNA is good but not as good as the previous two. They stick to it's wording too much. For example they will stick on paying customary and reasonable fees on procedures despite having top tier plan with them (so if your doctor is charging more, you will have to pay the difference). I am with Cigna now and no issues so far. I pay something around $4500 per annum. Premium also depends on your residence and country, so it is very hard to be compared on a global level.
I would try Luxembourg based DKV Globality, they seem to be tailored for expats, have good benefits and reasonable prices, but they can only offer insurance to UAE residents in addition to the local coverage, which is a bit pointless in my view.