I cannot speak to the W or its location from personal experience, but I stayed at both the Sheraton (which is connected by lobby to the San Cristobal Tower) and the Grand Hyatt in February of 2014 in Club rooms. Nice stays both, but the rooms were a little dated, albeit clean and plenty serviceable. The Club lounge was closed at the Sheraton (they have since emailed me to tell me they are refurbishing it and will re-open it) so they sent me to the San Cristobal to use its lounge. Neither hotel is close to much action, although a 5 minute walk across the Conception bridge will take you into Providencia from the Sheraton/San Cristobal. A five minute walk from the Hyatt will take you to the Parque Arauco mall. There are restaurants in both places if you don't mind the walk.

Breakfast at the Hyatt was cold and continental. Someone wanted an omelet at the next table to me one day and they got her one from room service. It looked so good I ordered one for dinner the next day. Room service at the Hyatt is very reasonably priced, BTW. And the view from the club lounge of the Andes is excellent.

Breakfast at the San Cristobal was very good and you could order an omelet if you wanted. Much more variety than at the Hyatt.

I was less impressed with the happy hour snacks. Not much either place, unless you were into sweets, where the Hyatt had more variety.

If you are inclined to take the metro, it's a few blocks walk from the San Cristobal but a hefty hike from the Hyatt. I know, because I did both, multiple times. I think there is more to see in Providencia than Los Condes, if you are just there for a few days and wanting to walk around.

Rumor has it the W has a hopping bar and a great view. But someone else will have to comment on that, because I did not even get to that neighborhood this trip.