NAnt or MSBuild, which one should I use in an svn environment

Menu Tools → Options → Projects and Solutions → VC++ Project Settings → Build Timing should work.

I've done a similar investigation this week. Here's what I've been able to determine:

NAnt:

• Cross-platform (supports Linux/Mono). It may be handy for installing a web site to multiple targets (that is, Linux Apache and Windows IIS), for example.
• 95% similar in syntax to Ant (easy for current Ant users or Java builders to pick up)
• Integration with NUnit for running unit tests as part of the build, and with NDoc for producting documentation.

MSBuild:

• Built-in to .NET.
• Integrated with Visual Studio
• Easy to get started with MSBuild in Visual Studio - it's all behind the scenes. If you want to get deeper, you can hand edit the files.

Subjective Differences: (YMMV)

• NAnt documentation is a little more straightforward. For example, the MSBuild Task Reference lists "Csc Task - Describes the Csc task and its parameters. " (thanks for the "help"?), vs the NAnt Task Reference "csc - Compiles C# programs." UPDATE: I've noticed the MSBuild documentation has been improved and is much better now (probably on par with NAnt).
• Not easy to figure out how to edit the build script source (*.*proj file) directly from within Visual Studio. With NAnt I just have Visual Studio treat the .build script as an XML file.
• Apparently, in Visual Studio, Web Application Projects don't get a *.*proj file by default, so I had great difficulty figuring out how to even get MSBuild to run on mine to create a deployment script.
• NAnt is not built-in to Visual Studio and has to be added, either with an Add-In, or as an "External Tool". This is a bit of a pain to set up.
• (Edit:) One of my coworkers brought this up--if you want to set up a build machine using CruiseControl for continuous integration, CruiseControl integrates with NAnt nicely out of the box. UPDATE: CruiseControl also has an MSBuild task.
• Please see comments below for full and up-to-date discussion of subjective differences.