All three types of multipathing software provide comparable levels of reliability.
Where they primarily differ is in terms of performance via load-balancing algorithms.
Storage vendors, of course, claim that their solutions are better because they are more tightly integrated with the subsystem hardware, but the differences in efficiency and reliability are generally minimal. Storage vendors claim that they take advantage of API calls to query the storage subsystem to obtain traffic statistics. This allows the multipathing software to more accurately determine how to balance the traffic, and may also help ensure seamless recovery from a path failure.
However, VERITAS DMP also understands APIs for several subsystem vendors and can use this ability to load-balance more effectively. Of course, for JBODs and unsupported subsystems, DMP uses a simpler method.