I don't think it is possible to choose just one. I personally used quite a few. If you somehow managed to get me in a choke hold and demanded that I answer the question... then I would probably pass out. On the other hand, if you managed to get me in a Figure Four Leg Lock and demanded that I answer the question... then I would probably say Mastering EJB or Enterprise JavaBeans. However, no wrestling move could force me to choose between the two.