many buses passing through ipanema and copacabana go along the aterro do flamengo, run very frequently, and would be a better choice.   

flamengo beach and the aterro are not  considered safe after sunset, exception made for nights following special events such as new year's eve fireworks and concerts.

flamengo beach offers a spectacular view of the guanabara bay, combining in the same landscape the sugar loaf, the morro da urca, and niterói.