Our team is working on the upgrade from TFS 2010 to TFS 2012. However, our team members were confused about VSTS and TFS per our conversation.
Some said we use VSTS 2010 to develop the current project, but will use VSTS 2012 to develop another project. Therefore, the best way is to upgrade from TFS 2010 to TFS 2012.
To clarify their confusion, I spent some time drawing the diagram of our TFS upgrade path via one note. After our team conversation and this diagram, we are on the same page.