Quick buyers' guide to the ultimate bicycle lock

I was repeatedly told my bike lock (3kg armored cable lock from ABUS) is crap, should have a better one for my bike. I started reading up on the subject, here is a concise summary of my findings. See reference articles at the bottom. Just read the first 2 sections if you do not have time!

Principles

1.  If you leave your bike in a place without traffic and people the thief  can try to break your lock forever - and no lock can withstand that.
2. If you choose a crowded place to lock your bike lock only has to take longer to hack than the one on the next similar bike - they will pick the easier to break.
3. You should spend at least 10% of the value of your bike on your lock.

In my case my Kona bike costs somewhere north of USD1000, so I am supposed to look for a $100+ lock (the current one cost around $30).

The winner

Without further ado: buy hardened steel squared or hexagonal link chains with hardened steel integrated locks or padlocks: these swing away from the angle grinder, slip out of the bolt cutters, resist longer than any other kind except for the best U-locks, with which however it is pretty hard to find any object to lock to where I live (Budapest, Hungary).
Read reviews before making a choice on the specific models: chain locks can also have weak points ("He found a weak link in the HipLok L1 Lite, snipping the shackle with bolt cutters in 29 seconds.").

Caveat emptor: these are heavy(!!!) and rattling pieces, you will have to wear them or put them e.g. into a backpack, cannot really fix it on the bike while riding.

Good examples

1. ABUS Granit CityChain X-Plus - 1.9kg (85cm) - 3.7kg (170cm)
2. OnGuard 8020 Mastiff ("hardened-steel links withstood a hacksaw and bolt cutters. After nearly three minutes of use, the battery in Ruzal's angle grinder died before he could cut the shackle") - 7kg
3. OXFORD NEMESIS MOTORCYCLE ULTRA STRONG CHAIN and PADLOCK 1.5M - 9kg
4. Blackburn ATTICA CHAIN AND PAD LOCK - 6kg

Or by anything with a Gold Sold Secure rating, or anything with four or five stars here.

Major manufacturers: Kryptonite, OnGuard, Abus, Blackburn, Masterlock, Knog, and Avenir.

Second best

U-locks (or D-locks) are the second best choices, hardest to cut through, however if large, a car jack can easily inserted into it. The smaller it is (against jacks) the harder it is to find a sufficiently narrow but strong object at the right height to lock your bike to. :(
If you by this, choose one that is locked on both ends of the U part:

1. ABUS Granit X-Plus
2. ONGUARD Brute
3. Kryptonite New York Lock
4. Kryptonite New York Fahgettaboudit U-Lock
5. Kryptonite Evolution Series 4 

Most of them are up to 2kg.

Or by anything with a Gold Sold Secure rating, or anything with four or five stars here.

Not recommended

1. Masterlock Force 3 - long term problems reported (ref. no. 11)
2. TiGr - - easy target for bolt cutters and angle grinders (ref. no. 11)

Tools

This is what we are defending against:

1. Battery powered angle grinders: the most hardcore tool, quite fast, not quiet, but cuts through any metal with time:
   
2. Hacksaw: basically the hand powered version of the above, slower and quieter:
   
3. Jack: mainly used against U locks, quite fast and quiet:
   
4.  Bolt cutter: a cutting tool designed to yield a cutting force up to 100 times stronger than the force on the handle. Quick, quiet but clumsy:
   
   
5. Wire cutter: basically small, pocketable version of the above, whichever lock cannot withstand this is a lost cause:
   
   

Standards

From reference no. 6:
"Sold Secure is an independent organisation administered by the Master Locksmiths Association. Locks submitted receive one of three ratings: Gold, Silver or Bronze. These reflect the length of time a lock will hold out against escalating levels of attack. Bronze is a minute with basic tools; Silver is three, with a wider array of tools; Gold is five minutes with a more sophisticated array of tools. 

The largest manufacturers also submit to the German and Dutch ART1 to 5+ standards. These are a very tough standard and worth looking out for. Gold or high ART-rated locks can be more expensive but they may help you get a discount on your insurance if you use one."

References

1. Bike locking 101 in Hungarian - not fully agreed, but do not buy that they don't recommend
2. German test TV show, obviously biased towards / sponsored by ABUS
3. A quick comparison (only care about what is best recommended)
4. A New York based mechanic shows you how easy it is: cable lock cut with wire cutters - unbiased
5. Suggests u-lock for portability, however still chain is best for security and flexibility
6. An in-depth guide
7. Nice tips in there: GPS tracker and to use an additional cable for the wheel not hold by the chain
8. Some more chain locks
9. Shows that the fashionable Hip Lock chain lock is actually only Silver rated, still at the top of the league
10. How to lock it? with either a chain or a U lock
11. Another detailed write up