#an-94
First of all, I respect the choices; the Zip 22 is cool in its uncoolness. It's a hilarious disaster it exists at all! And I always have plenty of love for a good old Hi-Power.
So, to answer your questions proper:
Cool but impractical: AN-94

I could have answered the H&K G11 and talked at length about the literal precise clockwork that makes up the internal mechanism, but that wouldn't be fair - I don't think the G11 is necessarily impractical, just extremely complex and German.
But no, I'll go with the AN-94. It is really cool because of its 2-round burst mode that can reach about 1800 RPM, feeling so fast it feels vaguely like a single shot, when you actually fired two.
It is REALLY impractical for basically everything else. The internal mechanism is a nightmare that involves a pulley and a sub-receiver, and based on the limited information I have of people who actually fired it, it's not particularly reliable either.
It's a cool gun that sacrifices two of the things that made the AK-74 worthwhile (reliability and ease of servicing) in favor of its one cool feature, the hyper-burst system. I love it to death and I have terrorized TDM servers in Battlefield 3 with it, but my gosh I would hate to be the armorer in charge.
Boring but practical: H&K USP

If there's one thing that's consistent about me, it's my fascination with H&K.
This one is simple. I grew up playing Counter-Strike and CS clones. The USP, especially its .45 ACP version, was an object of fascination. When I learned about what a SOCOM was in Metal Gear Solid and realized the USP was a more practical version of it, my love for it grew.
It does exactly everything I like out of a pistol: it's full-sized, it is hammer-fired, capacity is decent, the original USP was purpose-built to shoot .40 S&W, meaning it's almost overly durable for 9mm and .45 ACP, it looks amazing with a suppressor on, and it has a safety lever that doubles as a decocker so I don't have to choose or mess with a trigger dingus like on a Glock.
It's also not anything special. It's boring. It looks blocky. The only thing about it on looks alone is "at least it's not a Glock." It's not even especially the most ergonomic or comfortable.
But I love it.