Best beach on the Pacific coast

Hi lmayo, 
Out of those three I would say either Tamarindo or Nosara. Flamingo is nice but there isn’t a lot going on there. It’s more of a relax on the beach type place. Tamarindo and Nosara are very different. Tamarindo has a more touristy feel with a ton of different restaurants, bars/clubs, shops, activities, etc. Nosara has more of a chill vibe and gives you the feeling of being somewhere pretty remote (it has a jungle feel). There’s still a good selection of bars, restaurants, and tours but nothing compared to Tamarindo. Hope this helps you decide. Enjoy your trip!