Any rooftop is good, but another good spot is along the river where you can get a reflection of the fireworks if you have a relatively wide lens. Hard to get bad photos from a rooftop with a tripod though. Closer to the city center might be better since you can see in all directions but there are a ton of fireworks in the South for sure.
edit: By the way, were you at the Hakka Homes bar (SOHO rooftop) the other day? I think I might have seen you there.