I am thinking getting a new Shuttle and am trying to decide if I should get another P4 or switch to the Athlon 64.

I want the system to be quiet so I am concerned about how hot the CPU gets. In my past experience the AMD processors have been hotter than the intel ones but I have been reading the prescott P4 is hot. I recently got a Sempron and it runs very cool so I am wondering how the Athlon 64 is.

Also is it true that it's not worth getting the Opteron over the Athlon 64 ?