We’ve certified TFS 2013 (and its subsequent updates) to work with SQL 2014. However, there’s a hitch. Because TFS 2013 shipped before SQL, the license than grants the right to use it with SQL Server only allows SQL Server 2012. Starting July 1st, we will be adding SQL Server 2014 to the list of license grants for TFS 2013. That won’t, apply to earlier versions of TFS though – we haven’t even tested those with SQL 2014.
Anyway, hopefully this will make your life a little easier if you want to use SQL 2014. Of course, you can keep using SQL 2012 if you like.