I assume with req/resp over http you meant RESTful web services. If you can make a choice, go for simple RESTful XML over http solution. Coz, you dont need any additional middleware infrastructure and in synchronous messaging your communicating systems are tightly coupled. More loosely coupled solution is a better SOA.
In case you meant otherwise, it is good to opt for a SOAP based web service or a RESTful web service based on your specific needs.
JMS is a viable option for service producers and consumers that can do messaging such as Java applications, Microsoft systems using MSMQ and mainframe applications that use MQ-Series. In practice, this works inside the enterprise and between close B2B partners. For generally consumable services, SOAP or REST is better.
Independent Consultant — Author, EJB 3 in Action — Expert Group Member, Java EE 6 and EJB 3.1