GIG
Do not stay in either Hilton. They are in poor locations all around, especially the one in Barra. If you absolutely have to, stay at the one in Leme, but be careful when outside at night in that area.
Arpoador is alright, but it's not my first choice either.
SSA
Been there and stayed at the Sheraton downtown. That was a really nice hotel. Rode the elevator all the way down from the top floor with just myself and Ney MG inside, and survived !!! Don't ask me to explain, as only a Brasilian would understand.
My opinion of SSA as a destination is unprintable here, except to say it was waste of my time and I will never go back except to transit thru the airport to the resorts 1-2 hours up the coast which I enjoy.
GRU
I usually only transit thru there. Don't know the city very well at all.