1) It depends upon the cigar. Most blends seem to have a size that is the best of the bunch.
2) It depends on how mych time I have to smoke. I hate having to put a cigar down before I'm done.
3) Unfortunately, sometimes it depends on what's avaiable for cigar budget dollars. Smaller= less expensive.

Overall though, I like a Cuban Corona or a Torp for the feel in my hand.