As a follow-up, I can tell you about one brand to definitely avoid. While at Wally World, I saw some "cups made for the Keurig machine" - (apparently they can't use the words "K-cup") from Grove Square. Was only about $7 for 18. Cheap enough.
Terrible. Tastes just like instant coffee, not even good instant coffee. I threw the rest away. Save your money! When I got home, I saw it even says "instant coffee" as one of the ingredients. Who wants to buy instant coffee in a K-Cup? I've decided that most of the time I will just use fresh ground beans and put them in the adapter, that works well, and you still get most of the mouth feel of French Press.