OK, the best is definitely arguable because everyone loves to argue about their favorite spot but these are my top three. In no particular order but each one for a different reason.
Kiosk De Tica

They also have a lot of toppings you can get in either your acai like protein, nuts, granola, and fruits.
Health Benefits of Guarana
1. High in Antioxidants
Big Polis
Av. Ataulfo de Paiva, 505 – Leblon
Av. Olegário Maciel, 348 – Barra da Tijuca
Big Polis Acai with protein and fruit in it or just an extra side of fruit will fill you up for an entire day.
You can get Acai with Whey or just generic protein. You can also get it with Banana or Strawberries. You can ask from the “bitido” (pronounced Ba-Chi-Do) which is blended in or “ao lado” which is on the side.
BIBIs Sucos is so common I’m not even going to include an address.
Warning: this picture doesn’t do it justice.
is a super popular spot to get acai but frankly, I don’t see what the hype is about. The only reason it’s making my list is that they make this acai cup with passionfruit creme in the middle, that although it sounds really weird, it is actually AMAZING!
A little peak at what an acai menu looks like.