Taj Palace is the old wing and post reno, it is back to snuff and still best bet in town for leisure. For business, the Oberoi is probably slightly better - and Oberoi service is now ahead of Taj in India.

FS Mumbai is behind both of these hotels for a bunch of reasons. Rooftop bar at FS is nice, and pool probably more contemporary than Taj, though. Lobby is not crowded with tourists because, frankly, it is very small. The footprint of the building is small, so there aren't a lot of grand public spaces in the hotel (which isn't always a bad thing).