Mercurial is the best balance of simplicity and provides a modern source-control tool.
You can use TortoiseHg which is very similar to TortoiseSvn so you'll have a low learning curve there.
git is a bit more powerful than Mercurial and it's a bit more complicated to use but they have very similar core features.
I don't see much reason to use any version control tool other than mercurial or git. If you have a shared/map Windows drive then you have what you need to get started.