An Abus Granit X or a Kryptonite fahgettaboutit, plus a cable to secure saddle and front wheel. Or one of each of the beastie D locks
Unfortunately, no lock is theft proof if the thief wants your bike and has the tools and opportunity
What bike is it? If I were you, I'd get a really cheap beater bike and a serious lock if leaving overnight in a high risk area
If this isn't possible, make sure the bike is properly insured and you adhere to the policy terms
Get it marked by the police and make sure the serial number and details are registered