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I think the trick is quantity and diversity/awkwardness of locking as much as quality for best security.
In a world where forgettaboutits can be cut in 20 seconds these days, its good to use a diverse range of locks on the bike rather than focussing on one mega expensive D. A disc lock on the front, a wheel lock on the back and a chunky D.
At home I use a gold chain/ground anchor and then actually lock other bikes onto it. Its such a tangled mess that it would be such a pig to even work out where and what needs cutting to steal the bike it wouldn't be worth the risk/effort.
Similar to user_dontfukinatmeAmey. Almax chain and either a D-lock or a Squire Stronghold. Out and about I usually D-lock the frame to something substantial.