In general, Abu Dhabi is cheaper. But its a whole different ballgame in Dubai so its not a fair comparison. And for what its worth, Dubai is more interesting. Abu Dhabi has its moments, but they are few and far between. Dubai has a lot more to see and do. Sharjah is a hop, skip, and jump away and some of the other emirates not much further. Dont miss the Islamic Museum if you go to Sharjah. My point is that unless youre just doing a mileage run (which in that case I would question why you would want a 5 star joint) then Dubai will give you more bang for the buck even if it costs you a couple more. There are a lot of 4 star places there that are very nice and significantly cheaper. Just an opinion, of course.