It depends what your criteria is.
If you do not have used the 3.x version before, or dont have it running in product etc. Then I suggest to start out with the latest release which is the 4.4 version.
I advice for Fuse4.4 . Since it has certain features which are really good. Like Camel-Blueprint, Which has ease of deployment options.
The big difference between the Fuse ESB 4.x and ESB 3.x is Fuse ESB 4.x is leverage OSGi to provide container service, which is more convince than Fuse ESB 3.x.