None are difficult...you just have to be paying attention as a flight crew.

The "descend via" STARs (DYLIN4, KORRY3, etc) are some of the most error-prone arrivals in the country.

The departure off RW1 @ KDCA also gets messed up on a semi-regular basis causing a P-56 violation; its not really complicated though, simply STAY OVER THE RIVER and you're good.

ODPs that aren't specifically given as part of the ATC clearance are often messed up...no big deal in good weather, but could be deadly in IMC.

The TEB6 is probably the most violated DP in the country...if not, its got to be right up there. Its an issue because it creates a loss of separation with EWR traffic.