If it just based on source control, I'd go with SVN. The AnkhSVN free add-in for Visual Studio has been greatly improved in its new release. Also, you get the source code for SVN and the documentation is great! They changed some arcane things in TFS 2010 Source Control, and without the source code it can be very daunting to troubleshoot. Plus, you are dependent on the MSDN team for pumping out the doc's and they do it on their own schedule and at their own depth.
That being said, TFS obviously offers much more than source control. It is an ALM tool. Combining it with work items, reporting, automated builds, gated check-in, automated testing, etc. can provide some very rich value that you can only get with connecting disparate tools with SVN. And of course, having the source for SVN is not a failsafe. I've gotten into scenarios with SVN where it would have still taken weeks to totally figure out what was going on.
So, I recommend you look at it from an ALM perspective and see if your company is going to use all of the TFS features or is going to with a best-of-breed strategy (e.g. JIRA).