I'm currently using the JAXB RI implementation from Sun and it works fine for me. I didn't experience any problems with this implementation so far. Of course this may depend on your use case but I personally didn't hear of anyone having trouble with JAXB which is caused by the RI.
Actually I didn't try any other implementations because the NetBeans IDE already includes the JAXB RI and gives you a nice wizard to configure JAXB (at least for Java SE and EE projects). For this I unfortunately can't tell you if you'd be better off with another implementation.
Joined: Aug 21, 2006
Thanks Marco. What kind of license does the RI have? Have you used it in production?