That was my first thought but assuming travel is not an issue (i.e. the departure location is not a factor) might be an interesting discussion as I've been looking for alternatives as well.

I'm partial to Jumeirah Beach which is about a 45 min taxi ride from DXB. Plenty of hotels/shops/restaurants in the area, water sports, Sky Dive Dubai etc. Dubai also has a lot of tourist attractions, malls, indoor skiing, the desert, etc.

There are definitely nicer beaches in the world but the combination of airport + other things to do is hard to match. It's just getting a bit crowded these days.