Don't exclude the Fahgettaboudit from consideration. For most people, it is a great size. It will fit around the rear wheel of your bike and a beefy steel post set in concrete, such as a parking meter, but leaves a minimum of empty space for inserting leverage tools.

When I park downtown a night, I ride a 30 year old rusty bike (that rides great) with a five pound u-lock to go around the rear wheel, and a two pound u-lock to go around the front wheel and frame. I try to park next to shiny new $2,000 bikes that are "secured" with only a cable lock. Which bike will the crook take first?