I've worked with Perforce for years, as well as Clearcase, Sourcesafe, RCS, PVCS, CVS and Subversion. More recently I've started using GIT too.
From this experience my opinion is that, for most purposes, Perforce is the best version control system for commercial environments. While not as simple, initially, as Subversion, it has a number of more powerful features, especially around branching and merging. The "lock by default" approach is generally more suited to this environment.
For personal stuff, small collaborative projects, small start-ups, or open source projects I find Subversion is better suited in many cases. They have different approaches, different ways of working. You can't just line them up on a scale and say which is best.
That said I hate ClearCase. ClearCase is usually forced down from above (ie a management decision).
For many of the cases where Subversion trumps Perforce many people seem to prefer the distributed systems like GIT, Bazaar, Mercurial, these days. From what I have seen of GIT they may well be right and I'm sure other posters will bear that out.