What mach said is right, really, plus the hacks have different aspects that make them good. I'll give you a very basic summary;
If you're looking for tough fights and interesting sprite changes, play Pure White and Pitch Black.
If you're looking for variety in your Pokémon choices, item pace changes and the like, play Blaze Black and Volt White.
If you want a balance between the two, try out Yin Black and Yang White.
That's probably the easiest way to sum it up. I don't know about Light Black since that sort of descended into forum hell, but I wouldn't be surprised if it makes a comeback soon.