For looks: Marushin Taurus Raging Bull
It's a revolver, enough said? Always had a thing for revolvers and this is by far the prettiest/meanest/badass-est airsoft revolver I've seen.
For practicality: ASG MK23 Socom
Not as "reliable" as the TM it's a clone of, but it's dirt cheap and robust. The mags are also built to take green gas (unlike the TMs) and can be found for a lot cheaper. Add to the facts that it is silent and very gas efficient, and you have a brilliant side arm.