MooTools and Prototype were battling for 2nd place with MooTools ultimately taking the lead. I wasn't surprised to "whichever" with a fair number of votes. That was certainly the boat I was in for a long time. Spry and YUI and the others didn't get many votes but certainly have their supporters (more power to ya).
I obviously love jQuery and will continue to use that when the situations arise in tutorials here on CSS-Tricks. But I am only one man here and it's a big internet. You should use whatever you feel most comfortable with.
I'll leave the poll up for a little while longer if you have yet to weigh in. Then we'll figure out some other fascinating poll idea. Ideas welcome in the comments!
NEW: I put up a page where you can see all the past polls, and actually still vote in them if you choose. Check out the new CSS-Tricks Polls Page.