I think Brian's answer is perfect, but let me be a bit more clear: the answer is none.
As others have said better, one crucial quality for material course is quality: if you had an excellent "closed" textbook and a mediocre open access one, you should choose the better one, for the sake of your students.
But in this case I don't think you can actually choose, and this is for the better: you can start off with an open access textbook, and you probably can make it better.
"Openness" of things boils down to their license. They are often (as said) Creative Commons:
- CC-BY-SA allows you to do whatever you want with the original material, and create your own derivative works without even asking, provided that you release your material with the same license. For example, Wikipedia articles have this license: everyone builds on the previous version of the page, the license persists, the article (often) gets better.
- CC-BY-NC allows you to do everything without even asking, provided that you do not have a commercial purpose. Brian's response hints that this is maybe tricky, but I'll come to that.
- CC-BY-ND is rare, but CC-BY-NC-ND is common: it is the strictest version of Creative Commons, and in practice you can use and share the material, but not have commercial purpose and create derivative work without asking.
This is important: you can't do it without asking.
Of course, you can directly ask the author, and I doubt very much you can't negotiate a way to use the material as you want. It is possible you'd have to pay, but this is the norm with closed textbooks.
Creative Commons are licensed used to share our creative works: the open access-open knowledge movement advocates for a more flexible copyright system in which people are allowed to share and build things together.
The only thing you should pay attention, thus, are the different licenses of the different materials involved: if you want to create a new textbook, for example, you should check them and ask/negotiate permission if needed.
Copyright-wise, things can't get worse than with closed-access content.
Hope this clears a little.