Pipa is better in that regards, but as Sambachula has pointed out, there is a difference of scale. I like them both. Natal has cultural and historic sights that you won't find in Pipa and a few wonderful restaurants such as Camarões, Mangai and Fogo & Chama.

Thx. SambaChula & Luademochila,
Am I correctly interpreting your comments that aside from the ambiance/city vs village situation that both beach areas have good swimming (not surfing :-) ) areas that are clean and relatively safe (riptides, etc.)?

Yes, that's correct. Either Natal or Pipa have swimming areas that are clean and safe.

If you have to choose:

Pipa is rustic, calm in the day, yet bustling at night. A good place to go if all you want is to lie on the beach or swim. If you are an urban person and want a mix between beaches, culture and historic sights, stick with Natal.