Evolution series u locks are nice and light in my opinion. Can be mounted easily to frame,stashed in panniers, backpacks and even back pockets. they offer a great compromise of weight and security in my opinion for most people. The NYC series is the next level in terms of weight and security. Much heavier, more secure and I would highly recommend if you can leave it at a rack with seldom need to transport. $20 more can get you a krypto cable which I use for wheels in conjunction to u lock.

cheers,

Kelvin