Keep in mind that I have a biased opinion because I made Vex Foundations I & II, but here's why I'd recommend my course alongside CG wiki.
Matt Estela has done an incredible amount of work. CG Wiki is very comprehensive, accurate, and full of many of the same ideas I teach in Vex Foundations I & II. Because of that, every Houdini TD ought to check it out because it's essentially $200-$300 worth of highly-skilled work provided for free.
But - here's the catch - CG wiki is a collection of journal entries rather than a fluidly designed course. You don't get an awesome looking project, course files, feedback, and help if you get stuck. And that can be important if you're trying to learn something that's a difficult topic such as coding in Vex. It's not just reading what the content is - it's about how the content is taught.
If you're someone with a computer science background, then Vex Foundations I and II is probably not for you. It's probably quicker and easier to just go through Matt's wiki, and then you can take what you already know about C-style languages from there. If you're 3D artist though - Vex Foundations I and II is the most approachable introduction to vex that you'll find anywhere online. And that might be difference between you getting frustrated and giving up on it vs. getting past that initial learning curve.
So my advice is to do both. Check out Matt's wiki after you go through vex I and II. It'll be way easier to read through it, and by the end that, you'll be exposed to two different teachers teaching you concepts which aren't easy to get at first.
Good luck!
- Tyler