submitting pre-prints at Tenure-track faculty application
Seems to me that (b) would be best. 

"Preprint" usually means something that is ready to be published, so don't send something that isn't of publishable quality. You'll likely be asked to submit a research statement or something similar, in which you can describe what you're currently working on.

If you have at least 3 papers (or preprints) that you feel represent quality work, then there's no reason to send fewer than 3.  Obviously focus on the newest and best ones, but even an older paper gives an indication of the depth, breadth and quality of your research program.