If you don't have to choose, it can't hurt to have both!
If you have to choose, PMI is an international professional organization with ongoing support for professional development. Also, PMI now has CAQs - Certificates of Additional Qualification. There are two for IS so far. These might be similar to Project +, but I'm not familiar with them. I plan to take one of the CAQ betas in the next few months.
What can you tell us about Project +?