I've used both for years. I prefer Perforce.

Advantages:

Perforce ClearCase Faster (check-in/out several times faster; Better tool integration capability ("real" labeling about a hundred times faster; pre/post-op triggers) ClearCase database, VOB, doesn't scale Better report generation capability (has well -- only about 2,500 files per VOB, a good query language and can easilly create Perforce can handle many times that very useful quality and productivity metrics reports) amount with no visible performance hit) Nicer navigation (per file graphical branch/ Easier to learn/use (no versioning of history view) directories making integrations easier; branches not sparse makes creation of views much easier; one CM person for more than a hundred Perforce users versus about one CM person for per 20 ClearCase users, a few small Perforce manuals vs a wall of thick ClearCase manuals) More reliable (when the ClearCase server is down all work/builds stop, with Perforce developers have local copies of all files to continue working, ClearCase supports local snapshots but is not the default mode; ClearCase frequently "hangs" when hundreds of developers are accessing a VOB because ClearCase causes way too much network traffic; ClearCase requires about 8MB memory per user on on the server and if swapping happens causes a UNIX server to hang requiring a system reboot, Perforce uses far less memory and doesn't hang on swapping; Perforce automatically handles text format conversion between UNIX and Windows/NT, ClearCase requires you write your own conversion scrit/trigger; Perforce atomic changesets help prevent failed builds because a developer forgot to check-in one file associated with a bug fix or feature -- is an extra cost add-on in ClearCase) Less expensive (around $500/user for Perforce vs around $1500/user for ClearCase -- double the price for ClearCase if using replication which isn't needed in Perforce because Perforce works well in a geographicallly distributed development environment; Perforce requires about one fifth the adminstration and support time and figure a senior CM/build person at about $100K/yr...)

-George