Below are the locks i use (i have never seen on lying broken on the streets in NL unlike pretty much 80% of other locks). They both recently tested as the best locks available by the 'Dutch Cyclists Union'. (Fietsersbond).

For some people that i pointed to the test it was pretty much shocking reading. The test mantains that all locks (especially wire/cable/cheap chains) are pretty much useless here except for hardened chains and some of the best U-Locks.

The ABUS chain tested way better and harder to cut than a Kryptonite chain (Kryptonite KRF2 CH100l) which was had much thicker links and was a lot heavier (not hardened very well). The Abus tested as being harder (pounds per square inch needed to cut it) than even the most hardened bolt cutter. So in theory trying to cut it with boltcutters would only result in the thief breaking his expensive tool.

The Axa SL-7 is a very convenient secondary /quick stop lock when you can actually still see your bike. It runs in NL for about E 17. The Abus costs about E30 to E 37.

The AXA is a tested dutch design refined over decades and used by many people in NL. The Abus was designed for the NL market. The dutch bike theft situation (particularly in the major cities) is suppossed to be one of the toughest/worst in the world, about on par with New York. The reasons for this are varied, for example it is no big thing to steal or buy a stolen bike for quite some people. It is almost part of the culture students do it all the time and people offer you bikes on the streets fairly often. This cultural thing has lead to people adapting by getting the best possible locks or old, cheap (but usually decent) beaters with cheap locks. Then when it gets stolen they are not bothered and get a new (stolen) clunker.
I am not saying this is a good system or that i approve it it all, just describing it.

I always use both locks if i am locking my bike for longer than a few minutes or it is not in my line of sight. So far i have been bike theft free for about 7 years. Before i adopted these strategies i used to get bikes stolen on a fairly regular basis.

Anyway, the Axa is mounted on my front fork when locked it immobilizes and locks my front wheel and the Abus lock goes through the frame, back wheel and some real sturdy fixture on the street. May sound like hassle but it isn't it is very quick actually as both locks 'click' shut and i can very rapidly y (un)wrap my Abus around my seatpost.

Despite my locks i steel feel it is prudent to 'ghetto' my bike. The most proffesional thieves use battery powered side cutters (gives lots of noise and sparkes though) or even Liquid Nitrogen to freeze the cylinder untill it is so brittle the inner part can be shattered. This type pf thieve is rare/"elite" and only spends their time and effort on the nicest bikes that fetch the highest prices. That means (mountain) bikes that have a lot of branding and logos and that look/are high end. So no problem there for me.

Hope some of that info is helpfull.