I'm for PhysX. Please consider 3 things:
- I think it's actually planed by ageia to release smaller drivers
- Most of todays gamers have already installed the driver because of some big, commercial games
- Just remember that what you get here is really next-gen and with the support of nvidida the possibilities of the SDK will even grow, such as graphics card support for physics simulation

As all these physic engines are grown up and stable, there are only small differences between them. But in my opinion PhysX beats all others.