Unless it's ABUS, I'd stay far away from combination locks. They're usually cheap, cheap, cheap components.
I've had one lock sieze on me. It was a seriously heavy duty, braided, cable lock manufactured by Giant that I used for winter commuting. The barrel keyway seized up, even though I lubricated it.
I've been using a fairly cheap Specialized cable lock for my everyday commuting. It seems to be good enough to stop any theft attempts to this point.
I also have a Kryptonite Fagghaboutit, but it's far too heavy to be a practical commuter lock, so I only occasionally use it.