If you have time to be patient, penetrating oil, light taps with a hammer and if you are careful, perhaps a torch.
If it needs to be out now, a pipe wrench. Carefully work it back and forth. This WILL cause cosmetic damage and could actually break the distributor, if you are not careful. A torch could help here, as well.
either method is a lot easier if the engine is out of the vehicle.
Lawrenceville, GA