I am in Brasil a few times a year. Mainly São Paulo - city and state - and Santa Catharina.
Part of the problem with Brasil is that is too big. 9 hrs flying from Porto Alegre in the south to Manaus in the Amazon. You don't want to spend 2 or 3 weeks flying.
I am not Rio's biggest fan (prefer São Paulo), but I guess most people want to see it. For São Paulo city, if you base yourself in Vila Madalena (around Rua Aspecuelta) you can get a pretty full bar/music/club experience - from samba to rock to Brasilian rap. A lot of it free in lively bars. Nearby there is an area (Alto Pinheiros) which is more sedate and older crowd. Baixo Pinheiros (around Faria Lima metro) livens up again with a younger clientele.
I think you have to see the Amazon ( before it disappears). You can base it out of Manaus. I have only ever been with Brasilians, who have arranged it all for me.
Further south, the Pantanal in Mato Groso (I think the largest inland wetland in the world) is incredible for wildlife. It isn't a competition but I probably saw more there than the Amazon (effin' trees). Then further south again are the Iguazu Falls. (as Elanor Roosevelt said when she saw it, "Poor Niagra"). The problem is that there isn't an awful lot else there.
I also like Florianopolis in Santa Catharina. An island just off the mainland. So you have the South Atlantic on one side, with very large surf scene; the inlet side facing the mainland, and Lagoa da Conceição in the middle with some great little places only accessible by boat for a night or two.
If you are spending time in São Paulo you can access pretty good beaches easily - 90mins and £50 by Uber to the Littoral Norte. This a series of 10 to 15 beaches. Mainly small pousadas (hotels with 10 to 15 rooms). Maresias is bit more clubby/lively. Nearly every other place is a beach with a handful of restaurants. It fills up Friday to Sunday as 10M Paulistanos try to get there. Avoid travel on those days. A 3Km beach can have 100 people on it during the week, and crowded Sat and Sun. I have visited 10 or more times (back in April), I have only met a handful of foreigners there. This is really a local destination. Littoral Norte is a surf region.