We are a mostly MS shop at work doing .NET LOB development. We also use MS Dynamics for our CRM app... all the devs are currently using VS/SQL Server 2008. We also use VSS, but
First off, see this post:
SVN vs. Team Foundation Server
As to your question about which environment better fosters TDD and such, my two cents is that the build management system matters much less than what's in the build file itself. Your Ant or MSBuild file should have the targets that do your testing. With MSBuild or Ant, you don't have to use MS's test suite. You can still use nUnit or whatever else you want. That means it doesn't matter if TFS is calling your MSBuild file, or if CruiseControl is, or if TeamCity is. The smarts are all in the build file and the tools you integrate with it.
My personal choice is not to get locked down into TFS's way of doing things, since you have a lot more freedom for a lot less cost with the wealth open-source testing tools that are out there. TFS is about to receive a major upgrade, as well. If you are going to go with TFS, my advice is to at least wait until 2010 is released. Concentrate on making your MSBuild files as good as they can be right now.
That being said, I must admit that TFS has one of the nicest build systems out there (2005 was terrible, 2008 was nice). Being able to easily customize notifications and the release process all inside .NET code was pretty cool -- you had a lot more central control over build and release policy than we did with CruiseControl.NET.
So I've used TFS and SVN/CCNet. I can't speak much to TeamCity. But IMO a build management system should be fairly agnostic to what is being built and how it's being built. For us, the extra control in the release management process that TFS brought us just wasn't enough of a bonus for us to justify the greatly increased administrative effort of a fully integrated TFS solution. Nor was it enough to justify the extra per-license cost of TFS, which can be significant.