It is a bit on the pricier side, but I had just had a bike stolen and didn't want to go through that ordeal again. I recommend getting a cable with it so you can lock up your front wheel as well..
It is better to get the shorter version, but I went for the longer one so many of the racks in the city make it difficult to get a lock through the frame, your back wheel, and the rack.
Pretty much any lock is pick-able, your just want the hardest one to pick. I liked this one because it lock both ends of the U which hopefully would mean twice as much work for a grinder.
A little more expensive but the Krytponite Evolution Standard lock is stronger than the KryptoLok. £70 down to £50 on Amazon. 8/10 security rating instead of 6/10.
When people say combo u lock and chain they mean two separate locks, right?
For example, I should get a standalone u lock and a standalone chain lock, as opposed to just a u lock + cable lock bundle?
As for locking it up, ideal placement is u lock through the frame and rear wheel and chain through the frame and front wheel?
Quand je faisais du velo a paris, j'avais deux anti vol de ce genre, un pour chaque roue + cadre et ce n'etait pas du luxe vu la faune autour...
I got the Kryptonite Evolution. I think it should fit most bike racks with enough room to comfortably lock your scooter.