You'll find more action (restaurants, bars,people watching) on the Ipanema Beach side which is a short walk or inexpensive taxi drive. The area is more up-scale and overall appealing than the Cococabana side of the beach where the JW Marriott is located. I think the safety warnings you constantly hear are somewhat overblown, although you do need to watch your back as in any large city.
Have fun - it's a very beautiful and interesting city.
Is too bad the JW is not on the Ipanema beach area, would be much better...JW is nice, but very American....suggestion, when you venture all over Rio, do not wear any jewerly, including watches,necklaces,bracelets, and rings...copy your passport and VISA, take maybe 50 reias, and a CC ...learn some Port, goes a long way