Stayed at the Conrad Centennial two months ago...very good overall (two executive lounges, pool, good buffet/menu at Oscar's, attentive service overall-save for the doormen and breakfast waitstaff). It's right by a couple of malls (not a shocker in Singapore), but in the vicinity there's not much tourist spot-wise. Then again, you're never too long a car ride away from somewhere.
Can't comment on the Andaz, save for it being near Arab Street, a burgeoning start-up area.