Hmm. I've joined stackoverflow just because of your question.
I have never used Perforce, though I have heard nice things about it, and therefore I'm not qualified to compare the two, or to really answer your question. However, I have used TFS source control (currently) and Subversion (in the past) and while I really liked the power+simplicity of the latter, I have developed a distaste for the former.
Here are a couple of places that talk about some of the negative aspects and frustrations of TFS source control:
http://www.nearinfinity.com/blogs/joe_ferner/why_i_dislike_tfs_-_team_found.html
_ttp://goingagile.blogspot.com/2008/04/evaluating-source-control-systems.html
(new user, I can only post one hyperlink)
Of course, TFS is more than just source control, and the work items, reporting and project tracking features are nice.