There's comparison information on http://www.zaxwerks.com. Two huge differences: ProAnimator works as a stand-alone without After Effects as a host. Motion controls for ProAnimator and Invigorator are also very, very different. Both have advantages for different kinds of projects. The aps share similar modeling and texturing abilities.
If I were you, I would do a couple of things - take a look at the website. Download the demos and play.
If you have specific uses in mind, we can make a more definite recommendation.