WSO2 has recently performed a comparison study by considering various metrics, and in all the criteria WSO2 ESB has been well performed!! It's extra ordinary speed against to a number of leading open source ESB. Refer WSO2 article on WSO2 ESB Performance Round 7.5 this for more information.
This comparison was made with WSO2 ESB 4.8.1 against Mule ESB 3.4.0, Talend ESB 5.3.1 and Ulatra ESB 2.0.0. The below shown in the final observations during this.