I have used both, but only as a developer (in java development) and never as someone tasked with setting either up. PVCS seems to have some difficult installation and set up (at my previous, there was literally one person who could install and set it up in an organization of a around 1000 people). The experience wasn't bad using it, however, there was no integration with any other tools we used.
SVN, on the other hand, at my current employer is integrated with our bug tracking software as well as our IDE. However, we use eclipse so I doubt there isn't a PVCS plugin.
The difference from what I have seen, is SVN facilitates and ease of merge from local to server based source. Multiple people can change files and simply merge at check in. PVCS, from what I've used of it at least, doesn't have that feature. SVN also is integrated with our bug / tracking system and will associate every change you check in with the current issue you are checking in for. I wouldn't say SVN, from my experience, is that much vastly superior than PVCS, but I am not very picky as long as the tool works.
Merging all your versions and branches from PVCS to SVN, I cannot comment on at all. This is something I have never done.