i've got an on-guard "beast" 5017 chain/lock. the whole setup is poorly made and >50% of the volume of the lock is plastic. crap. i've been trying to get rid of it.

i've also got a NYFU, a NY-STD and two bikeregistry chains, one with the standard lock and one with the upgrade lock (keyed alike, because those guys are awesome). these are all ace. i've also got a NY M-18W but that's so damn big it never gets used.

nothing will stop an angle grinder - some things will slow it down. depending on the bike, location, paranoia, weight concerns, etc... a NY lock and/or a bikereg chain (with the upgrade lock) are about as good as it gets... if they're used properly.

some of the high-end abus U-locks might be on par with the NY locks, but i haven't seen any in real-life.

every now and again, spray some dry-lube into the keyhole and into the hole in the crossbar where the shackle goes in.