What's the best bike lock for a high-theft city?

Across the reviewers we read, the heaviest hardened U-locks dominate for high-risk areas. OutdoorGearLab found the Kryptonite New York Standard (16mm shackle) virtually impervious to hand tools, cordless drills and even car jacks, though it conceded the angle grinder still defeated it. Community consensus on r/bicycling and r/BikeLA is that it's the best deterrent most riders can practically carry, at the cost of weight and bulk.