I'd say the Kiwi; I've carried smaller as a backup, but the Kiwi is the minimum I'd carry on days when I've only got a single blade on me.
(besides the ones on my keys or a SAK/Leatherman)
I carry bigger knives like the Mamba, Vallotton, Military, etc. on most days, but it's not like working in an office as an IT guy really requires me to
A tiger has claws,
A wolf has teeth,
An eagle has talons.
We, have Spyderco.
Grails: Abalone Mini Mariner
, Ti ATR, WTC, Ti Lum Tanto