I don't feel like I can tell much difference between U-locks.

I've got an OnGuard Pitbull that I leave on the rack at work. It started jamming after a couple of years (exposed to the weather constantly), but I oiled it and it's been fine for a year since. It's absurdly heavy, but since I don't carry it around that doesn't matter. The cover that slides over the keyhole seems like a nice feature. I also have a 5-year old Kryptonite of some sort and a Kryptonite-made Trek Streetwise. The Kryptonite gives me trouble sometimes with the rubber ring that holds the bracket attachment coming off. I have no complaints about the Trek Streetwise. It's light, doesn't fall apart and has a keyhole cover.