Small condenser mics is definitely the way to go. If the piano is the main instrument, use two mics (panned left & right). If not, use just one mic. Move the mics around the piano until you find the "sweet spots" where it sounds really good. For me, one reliable place is usually about 5 feet off the ground facing the front of the piano and pointing at the highest key. This prevents the undesirable keystriking sound from being too prominent, and gets an accurate signal (move the mic backwards if you are getting too much low end).