For classical, you can't use a magnetic soundhole pickup like the Seymour Duncan Woody, Dean Markley Promag or Fishman Rare Earth. These use a magnetic field, while the classical guitar's lower three nylon strings are nylon and won't generate any magnetic field (not sure how to put it, I'm not an electronics student).
It's either UST (Under-saddle transducer) or microphone direct. I've seen microphones that can be clipped to the sides of the soundhole, but they are microphones and thus have the same drawbacks as microphones placed near the soundhole, but at least you can move around as much as you want.