Please take a look around the forums before posting, theres tons of threads that explain how to get started. As for whats most profitable, fun, and best in all, there is no hard answer. For profit, look at job projections (i think software engineers make the most, but that takes a degree) if your asking about profit in an illicit manner, then I *cant* say for sure, but I would *imagine* it's limited by your ingenuity. Not that I'm promoting anything illegal here.
For fun, it depends on what you consider fun. Personally I'm not a huge fan of websites, the code gives me a headache too look at, too much UI related stuff. I prefer looking at more of the software codes instead, but I know others who prefer websites and find site related vulns to be the most fun. As for best in all...thats like asking what sport is the best in the world, theres plenty of opinions but no straight "this is the best" (totally would be soccer
) you just gotta find what you like, if your really that interested that is.
Cheers man