Depends which time of year you will be coming as well because the Old Clare has a rooftop pool too that could sway your choice. There's a "hop on - hop off" tourist bus stop adjacent to OC so if you're inclined to do all your tourist'y things in one or two days, it's perfect. There's a few galleries walking distance to the Old Clare, I like the White Rabbit Gallery (
http://www.whiterabbitcollection.org/), it's free and the themes change periodically. Also around Surry Hills there are regular boutique/small art gallery openings where you can view art and enjoy complimentary wines and hors doeuvors - you know where I go when I am thirsty
. Either choice you won't go wrong, the Westin is a very nice (business) hotel.