Try to determine if it always sticks in the same spot, which may narrow things down a bit. Could be the cylinder like you mentioned, or the dreaded control valve as the most likely candidates. Lower on the list would be the pump and steering box. Personally I've rebuilt a tired control valve, but the cylinder is all original. Also, maybe something is bent.
Might also be alignment. Although, a few parts could be worn causing the misalignment problems which are causing the sticking. Does it stick at full deflection or just at a certain spot of the steering wheel rotation?