I'll say with some confidence that there is no "best" in this regard. Your development process has support requirements; your version control should support them to the maximum extent possible. The big tradeoff will generally be functionality versus license cost. Not knowing how many users you would have, what your configuration item mix looks like or whether you're in a WAN-distributed environment it's had to say much except Source Safe is unstable garbage that is useless in a distributed environment without third-party add-on kluges. Describe your environment in more detail. What do you find to be shortcomings of PVCS?
"Debugging is twice as hard as writing the code in the first place. Therefore, if you write the code as cleverly as possible, you are, by definition, not smart enough to debug it." Brian W. Kernighan