it doesn't particularly matter, so choose either.
Things to bear in mind:
1. Java is a 'language' Flash is a software product.
2. Java is object oriented, Flash isn't.
Web designers like Flash because they can design Flash animations themselves, whereas most of them can't write Java - therefore you see tens of thousands of Java applets which have been written by third parties and made available as downloads for use on websites.
The Java versus Flash argument has been going on for years - certainly since I really got involved in web design, and that was in 1996. Everyone has their point of view, and the best way I can sum it up is by saying that Java is probably better, but Flash is much easier.