What Java Message Service Implementation?

alapalaya queries: "If you had to implement a message dispatcher with soft real time requirements, which has to manage a lot of messages, and in general subject to a lot of problematic requirements (including object persistence); all implemented using a Java Message Service; what implementation would you use? In fewer words: in your opinion what is the best Java Message Service Implementation? Among the various JMS implementations I am currently using SonicMQ; but it doesn't seem to scale up in a proper way (to around several hundreds of clients generating from 10 to 200 messages/sec each). What do you know about other vendors/implementations?"