As someone with 45+ years of experience in the Transaction and Message Processing world, I have seen many "MQ" solutions that have come into the market place. From my perspective, while each product has its sweet spot that it tries to address, IBM's MQ (aka MQSeries) is the only one I would select to build applications upon.
The reasons are many, but just to note that IBM MQ has been around for 28+ years, runs on many different platforms, allows one to use just about any Programming Language and has the support of a very dedicated set of smart and passionate professionals who continuously enhances its capability so that it will be around for the next 50+ years., tells me that I can't go wrong with IBM MQ as my one and only Messaging Middleware.
I know that cost consideration drives many decisions, and there are so-called "free" alternatives to select from in the MQ market place, but ask yourself, is there really anything that is truly free that is worthwhile investing in?
The importance of being able to assure that messages get to where you send them, once and once only is often overlooked, and if one focuses on what is really important, you will find that IBM MQ is worth every penny you pay for a supported licence version for your Production Environments.
IBM allows the "no-cost" use of MQ for Developers, and this is a good deal.