Despite all of the choices we get nowadays around messaging, including cloud solutions offered by Amazon Web Services (SQS) and Google PubSub, Websphere MQ still remains the top choice for Enterprise applications requiring reliable messaging. Based on some recent performance reviews, seems like purchasing Websphere MQ license is worth an investment.
Here is a good performance review of IBM Websphere MQ v7.5 vs Apache ActiveMQ 5.9 by Roman Kharkovski.