Sorry for being so late....
If I had a choice.... I'd only collect ERROR notes. Why? Not all error notes are the same, there are so many varieties out there that are known and unknown. That's what makes it fun to go online, go to local shows, and come onto forums, such as this one, and see the amazing specimens that exists.
Its always fun to pull them out and look at it and just imagine how something like that could have come to exist and how it managed to fall into your lucky hands. The WOW factor and the rarity of these are also factors that makes Error collecting fun and exciting.