>>1782111skilled attacks are rare
Vast majority of bike thieves will have cutters, ranging in ability.
The cheapest/lightest cable locks won't stop anything. But they do keep honest men honest.
Your better cable, chain, and folding locks will resist some cutting attacks. Which is a worthwhile step up seeing as very petty thieves are the most common.
A d-lock should resist all 3, though some will go down to larger boltcutters. And an angle grinder.
The fatal flaw of a d-lock is that it's weak to leverage/prying attacks. If you have a bar, which can be found on the street, or even just with the frame of a bike, most can be popped open.
That makes the most secure type of lock a mini-d lock, because there's less ability to fit a lever in it, or to use the bike as a lever.
But, mini d-locks are the least useful type, for the same reason their security is so good. There's no room in them. They really require a close well designed bike rack to lock to, most random street furniture will be too far away.
The solution to this is to have a mini d-lock AND a cable. When you don't have a suitable bike rack, use the d-lock to lock the rear wheel (so the bike can't be rolled or ridden) and use the cable to lock it to something.
But really I think every type of lock is valid it just depends on your priorities and circumstances. And where you leave your bike is more important than what lock you use
