I currently use nant, ccnet (cruise control), svn, mbunit. I use msbuild to do my sln build just because it was simpler to shell out.
Are there any merits to switch
The most compelling reason to use MSBuild (at least in .NET 3.5 and beyond) - the build engine can build concurrently.
This means a huge speed up in your builds in you have multiple cores/processors.
Previous to 3.5, MSBuild didnt do parallel builds.