What's the most challenging U.S. airport?

Oshkosh during Airventure!

+1 for Aspen. Aspen makes DCA seem practically normal.

Tellerude in the winter.

Since this is titled challenging as opposed to rare, post 911, I contend that KASE (Aspen) is by far the most challenging airport in the country. It is surrounded with cummulo-granite, all approaches are circling minimums only, no category D approaches authorized, on and on. For you IFR types, look at the approach plates. The descent rates are high, the minimums are high and the escape routes are tricky. Best be on your game when you go there as snow is common, icing is common, winds are common and in ski season, you won't be alone. And, in ski season you need a reservation. I have flown into ASE in VFR conditions with new guys and most are stunned that there is even an airport there. Ah the rich, they want to be where they want to be, when they want to be there. Google the Aspen accident reports. There are plenty, and many are turbine airplanes with professional crews. Telluride is no slouch, nor is Tahoe. Reagan is simply flying the procedure. Oshkosh has the best controllers in the world, and all volunteers to boot. Just do your homework on the procedures and pay attention. N numbers mean nothing at OSH when the show is on. Aspen is listed as one of the ten most difficult in the world, let alone the US. Reagan is just a hassle. And if you want a busy, challenging hassle, go into KTEB. Could go on, won't.

If we're talking Part 139 airport, maybe, but I contend that there are other GA airports out there that have some more difficult approaches...

I totally agree, but my response was referring to an airport with some similarity to what the original poster cited. If you want to interpret the post in a literal sense then you open a whole new can of worms, I.E., used by what aircraft type, pilot skill level, paved or unpaved, etc. My response was of course, subjective, as there is no definitive answer. A response from most of the posters on this forum would comprise a very long list of airports that most would have to look up in an Ac-U-Kwik and some would not be there.

Regards.