I use a Fahgettaboutit on my commuter folding bike.
The Fahgettaboutit is unique in the Kryptonite line as it actively locks both ends of the U. It also prevents the ends of the U from turning. To defeat this lock by cutting requires cutting either through the U twice, or through the crossbar. The On-Guard locks have this feature on most models, but they have a reputation of not being quite as reliable as the Kryptos.
The orange Kryptos are also good. I think the smallest orange one is the preferred lock for NYC bike messengers.
Instead of two locks, you can use one U lock and a cable with eyelets in each end. These cables aren't expensive. You could also use locking quick release skewers on your wheels (especially the front wheel).
I dislike cables even beyond their cutting vulnerability: They are always trying to coil back up. It takes a long time to weave a cable through a bike. This makes one want to skip using the cable for quick stops. Of course, that's when something's going to happen!