I'd probably get the 8 1/2" ruler. I think that some of the smaller ones might be too hard to keep in place as you're cutting. I don't usually cut to a sixteenth, but I can see where these would be useful if you did.
Here's the URL in case anyone wants to see them:
http://quiltersrule.com/Rulers/simple-strips.html (I don't have any connection to them.)