Who wrote the most and least of the Bible?
Well, Jude, written by Jude, has only 613 words so he would probably win if you were looking at total output of books to determine the smallest. However, Psalm 88 was written by Heman the Ezrahite, and is 296 words long, so I vote for him.
There are 17 anonymous Psalms, but we can't necessarily pick one of them as Hebrew tradition says they may belong to whoever wrote the previous labeled Psalm.
As far as the longest, by book count that would be Paul, but by word count that would be Moses.