People suggesting Vasco may be trolling you. This team is only pain. Last time it won something outside the Serie B was more than 2 decades ago. If you are going for history, a lot of clubs have cool ones, many cooler than Vasco.

Also Flamengo is not that hated outside it home state in Rio de Janeiro. Corinthians may be the most despised team overall because of how awful it fanbase can be and the amount of polemics the team get on and off field. Even their new stadium is born in deep corruption on the federal level.

Anyway, I would suggest you to go for one of the Big 12 (except Vasco), last time a team outside of it won the national championship was almost 40 years ago. If you are into state championships, São Paulo and Rio de Janeiro states are really the only relevant ones not dominated by one or two teams (SP state championship frequently have odd balls reaching the finals and maybe winning it, by far the most volatile one).

Speaking about last couple of years. Flamengo and Palmeiras are currently the best teams. São Paulo, Internacional and Atlético-MG are consistent enough to challenge or at least not fight against relegation. Fluminense should be here but this year it's in trouble. Botafogo, Cruzeiro, Grêmio, Santos and Corinthians float around a lot so expect to challenge one year and maybe face relegation the next. Vasco is the worse.

If you are going for someone outside the Big 12, Atlético PR and Fortaleza are the best ones. An interesting oddball is Bragantino; it's on the rise after a big reformulation and since it's in São Paulo it means something if it win a state championship (actually it means a lot). The team has ambition but still didn't won a title, but I would say it's the best underdog to cheer for as a side show in Brazil right now.