At work, a 3-1/4" Buck 303 or a 3-3/8" GEC Conductor is hardly noticeable and about as small as I'm comfortable with using for most simple day-to-day tasks. Those make a great office pocket knife.
At 4-1/4", my Buck 112 is the smallest that gives me what feels like a full four finger grip so that gets weekend time when I want something substantial. Its my favorite workin-at-home pocket knife.
I've been on the hunt for some alternatives that fall somewhere in between these two. Lately I've been warming up to my Opinel 7 since I can get four fingers on it even though they are a little crowded. I got my eye on that GEC #72 though as it seems like it would be a nice compromise for me between pocketability and comfortable grip.