Hi Monica,
Between those two places, we’d say Playa Pelada. Nosara has lots of good restaurants, beautiful beaches, and you can go fishing from there. The Pelada area is also quieter- Tamarindo will be busy in December, especially if you’re coming around the holidays. The only thing to keep in mind is that the beaches around Nosara are better for surfing so have bigger waves. You can swim at Playa Pelada though; you just have to be careful of riptides. Here’s our destination guide to Nosara with lots more info if you haven’t seen it already: https://www.twoweeksincostarica.com/nosara-trip-planning-essentials/

One other town you might want to look at is Samara, just south of Nosara. It is even quieter than Nosara, has calmer water, and also has the rest of the stuff on your list.