FWIW, I've acquired over the years two sets of Sennheiser NCs (PXC150 and PXC300) as well as the Bose QC3s.
The Sennheisers come in a much smaller package than the QC3s (and are cheaper). Additionally you can use the Sennheiser as a normal set of headphones without turning on the NC functionality (e.g. if the batteries are flat). the Sennheiser's take normal AA batteries, so you can get new batteries pretty much anywhere in the world.
The downside to the Sennheisers is the overly complicated system they use (jack to battery compartment to headphones). I find the cables tangling up all the time, and getting them out/packing them away is a PITA sometimes.
The QC3s are very comfortable, and cancel noise just as well as the Sennheisers. They are easier to pack away. However the case they come in is enormous (in comparison), and the battery must be charged to use it.
The QC3s cost $599 here in Aus, but only US$349 (+ state sales tax) in the US, so consider buyng them in the US (given the current exchange rate). Note that the US package only comes with an adapter for US power points, whereas in Aus you get a range of different adapters.
HTH