I work for a major package carrier so I'm out in the public alot and pull out and use a knife quite often. I live in the city and people aren't quite comfortable when you whip out a 4 inch blade even for a menial task. I try to keep it 3 inches or less and since I'll be beating on it try to keep it on the cheaper end (afraid I'll lose it too with all the moving around and in and out).
Right now in my rotation I use a Skyline, Mini-Grip, Delica, Mini Recon things in this category and price range. Just work knives that stay in my locker, after I punch out it's a whole different ballgame...