They're used for different things. What's your goal? HCG is usually used to combat testicular atrophy in the middle of a heavy androgenic cycle. Other than that, it just causes more inhibition of natural test production. M'kay.
Clomid will restore your natural test production fine by itself most of the time. I don't advocate HCG use myself. Produces as much estrogen as testosterone and only mimics LH. Doesn't really sound like a better option then clomid to me...