I prefer each one differently, it depends on the purpose of the tank (I know, not what you wanted to hear, lol).
Blue looks great in a fish only. Black looks great in a reef. Foam rock walls, when done right, look really nice in Fish only, when you want it to look a little more natural, and not just like another boring fish tank. They also look great in seahorse tanks. I've seen a couple really nice reef tanks that are aquasquaped with three islands of rock work and in between the islands is the foam rock wall, they look awesome. Most of the time, I prefer just plain black for a reef, but if the foam wall is done correctly and doesn't take away too much space, they look really nice.