We used Dive Palancar when we stayed at the Allegro in 2009, and then again when we stayed at the Aura in October (and we did have to pay the pier fee when we didn't drive to the Grand). Prior to 2009 we had used Dive Paradise multiple times, but really loved Dive Palancar and have switched to using them. The staff was great and very professional, and the boats were not crowded.
I only have one experience with Sand Dollar, but that was in 1998 on a dive from a cruise ship, and I've learned since then to stay away from boats full of cruise ship passengers!