Am I getting this right. PhysX is supported by Nvidia by their hardware, so the gpu can calculate part of the physics?

How about Havoc, is it supported by any hardware?

If not, I'd say PhysX is the better choice because it is supported by about have of all graphic cards and about the same as Havoc for all the others.
It's better to have some supported hardware then none as long as it runs good enough without the hardware support.