Forget about the THX Optimizer. Without the color filters that come with actual test discs, you have no consistent way of calibrating the video settings. If you're looking for basic tests and some tutorials on how to properly do the setup, then I would recommend the S&V disc. It's much easier to use than DVE, and is a great place to start.

The DVE disc contains more advanced video tests and rather than just using a blue filter, that disc uses three color filters for doing the video settings. A lot of the DVE video tests are good only if you know your way around your TV's service menus, so there's a lot of advanced stuff on there that you may never use. I've used both discs and for my TV at least (non HD, direct view set), I've gone back to the S&V disc because of its simplicity and minimal time needed to verify the settngs (the menu system on the DVE disc is very confusing). If you have a HDTV with more settings to adjust, then DVE might be a better choice.

I haven't used the Avia disc, but some people like it better for video tests. However, for audio tests, Avia's a little long in the tooth because it has no DTS tests and no 6.1 format tests. Even the S&V disc (which along with the Avia disc is made by Ovation Software) has those audio tests.