The VG Resource

So Source games use .vta (vertex animation) for model expressions.

Now I was wondering for HL2 rips, should I use a .vta, or a blender file with the model already imported with the .vta?

If I were you, I'd include both. I say that because some people want the original source files, while having the blender file included for those who don't know how to work with source.