I would have to suggest DJ
Java Decompiler (
http://members.fortunecity.com/neshkov/dj.html). I have never encountered code which it cannot decompile. Plus, it's written in c++ (I think) and it is very fast. I dont think it needs the SDK or even the RTE for that matter.
However, I have encountered code which it generates uncompilable code for (only code run through an obfuscator first) because some of them obfuscate and add in labels which screw up the compiler. Hope this helps.