Attached Link: Poser Comparison Chart

The link should give you more precise information.

Poser 9 is newer than Poser Pro 2010, and thus has more features.

 

As aeilkema stated, if you have a 64-bit version of Windows and more than 4gb of memory, Poser Pro 2010 will be able to take advantage of that, but as LaurieA stated, Poser 9 has SubSurfaceScattering; though not Gamma Correction which is limited to the "Pro" versions and Poser 10.

Plus Poser 9 has IDL and rendering speed improvements over Poser Pro 2010, so that's something to take into account.

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If you're joking that's just cruel, but if you're being sarcastic, that's even worse.