I have been a happy Ursack owner for a few years, and I doubt I will ever use a hard-sided cannister again. The lower weight and convenience of packing a bag vs cannister have me won over.

As far as reliability goes, the latest generation of Ursack bags are proven bear-resistant and certified by the IGBC, and there is actually growing evidence that these bags are actually more "bear-proof" than hard-sided canisters (see reports coming out of places like Yosemite where bears have broken dozens of canisters).

Some people still express their doubts about using the Ursack bag, but I would encourage people to ask advice from people who have actually used/owned both - in my circle of friends, I don't know a single person that favours carrying a cannister anymore.