Anatomically speaking, excluding all other factors, the penis is
much easier to access than the clitoris (yes, I have a talent for pointing out the obvious
).
If you factor in personal preferences, willingness, skill, sensitivity, size, hygiene, orgasms, etc., the answer to the "harder task" question very much depends on the individuals involved.
FWIW the first couple of times that my wife gave me BJs I couldn't get off because I didn't know how she would react to me coming in her mouth. Once she assured me that she wanted the experience I was fine. OTOH, she had no problems orgasming from cunnilingus once we sorted out which techniques felt the best to her.