I don't know if you've already figured this out or not, but here goes.
I can't really answer about Biztalk and Rhapsody, but I can talk at great length about JCAPS, so I hope this helps.
First, I've been a java and JCAPS developer for 7 years in an enterprise with about 10 other developers and many projects that live on JCAPS. In it's simplest form, JCAPS is really just a bunch of plugins and layers that create enterprise java applications for your using business rules that you define.
Second, JCAPS is basically dying\going away\EOL. I'd look for\pick just about any option that will suit your needs, or start looking for someone who knows it: it's not exactly trivial to pick up on your own.
Lastly, we've been down the ESB selection route and that conversation supersedes an answer on SO. It's a long and complex topic that will vary on many things: size of your organization, how your ESB will be used, who will be using it (BA's, Devs, Operations), how much you're willing to pay, what kind of support you need, what kind of backing technology you have on site, and much, much more that I am probably missing.
I hope this helps!