Re: dive sites. This would really depend on what you like to see; macro, pelagics, wrecks, drift diving etc etc. Bali diving has something for every diver with dive sites to suit all experience levels.
If you can drop me an email at the address mentioned above, telling me what level certification you are, when you last dived, and any other info that might be helpful, I can give you a quote for a diving day. Will you be diving alone?
To answer your other question: The night diving in Sanur is alright, plenty of things to see.