You've got things a bit confused.
1) Bitboys came up with EMBM
2) Cube mapping is a form of enviroment mapping
3) You are referencing dot3 bump mapping
To answer the basic question though, they both have advantages in different situations. Now I've not a lot of experiance with actually using them, but I believe dot3 is a bit easier to use (take a few textures, do a dot product op and you are all set). However, one of the key advantages of EMBM is that it can produce realistic pixel-level shadows from the bump map, which dot3 can't. So it just depends on the situation. They both look really good, if they are done properly. Which is better all depends on the situation.