Normally for me any chord is really easy, including the barre chords, but the chords that really give me a pain in the neck are the movable chords (used mostly for jazz) On chord in particular is th Gm11 movable chord:
e--x--
B--1--
G--3--
D--3--
A--x--
E--3--
Its might not seem difficult, but there are alot more of those!!!