The chances of having a problem with a bear go up with the amount of time you spend in bear habitat. If you don't live in a place where a bear might chase you into the house as happened to a local fellow here recently, then your chance of having a dangerous bear encounter are less than might be the case here. Conversely if you are in the business of providing bear security to the public, your chances of having a dangerous bear encounter increase exponentially.
I don't like buckshot for big game. I carry some in my side saddle in case my dog gets badly injured and we are miles from help or in case we cross paths with a rabid fox. Other than that the use of buckshot is a very specific one, such as when a bear must be destroyed in a crowded area such as a town or a congested camp site. It is unlikely that the pellets would exit the target so buckshot is a better choice than slugs in such circumstances, although naturally any shooting around other people must be done with greatest of care regardless of the circumstances. The light individual pellet weight from buckshot and the low impact velocity are what limits penetration. If the range to the bear has caused the pattern to open so that it causes multiple minor wounds rather than a single massive wound, it's effect is greatly diminished. Expect to have to shoot more than once and probably several times.
If you carry a shotgun for bear defense, slugs are the correct answer to the ammunition question. I like Brenneke, but they are factory loaded to a lower velocity than either Federal or Challenger. They also have lighter recoil, so if I have to make a fast follow up shot it is quicker to get back on target than with faster slugs. The wound cavity from the Brenneke has been discussed at sufficient length that it does not need to be repeated here. Perhaps they have the best balance between weight and velocity to ensure maximum penetration, where faster slugs might either break up on large bones, or limit their penetration due to excessive expansion. Having said that Garry Shelton, as bear wise a fellow as you are likely to meet, thinks highly of the Federals. My complaint against the Federals is that the deep set primer might result in misfires in some guns, as they say the scariest sound in the world is a click when one expects a bang.