Java is the way to go for me. I find most of the apps i use are Java based. Here is a link to <a href=”http://na.blackberry.com/eng/developers/javaappdev/javadevenv.jsp”>Blackberry’s JDE</a> I guess in the end it is what you are most comfortable programming in.
I think either one would work. I haven’t seen a ton of new apps for blackberry compared to the iphone or android but over time i am sure one will become more popular than the other..