Well here is my two-cents worth.
I'm a outfitter for black bear and have seen many different setups that people bring up. I really try to steer my guests into shooting a fixed blade if they can get it to group. Thats the key....they have to group. You owe it to the animal you hunt to have you and your equipment in tip top shape. Take the time to tune your set up....believe me I see alot of people that don't, and just take the easy way out and grab a pack of expandables on their way up to hunt. As much as we send info to the hunters and talk to them on the phone, this allways happens with a couple of hunters a year. Your typicall shot at a blackie over bait is going to be about 10-12 yards. Most people should be able go get a fixed head to fly and group at this distance. However if you try and try and just can't get a fixed to shoot well, an expandable will work. Don't get into the large cutting width heads though. A good bear could have a good 2" or more of fat on them in the fall. That fat I beleive takes alot of energy out of any head, but more so with an expandable. And some of them don't quite open fast enough to leave a good entry hole. Couple that with no exit hole and you have a bear that is very hard to track. Go with a small cutting diameter with an expandable if you find you can't get a fixed to fly. I actually have on video a shot that a guest put on a bear with a spitfire expandable. On the video you can actually see the arrow deflect once it hit the bear and go straight up! The hit itself was a little high on the bear and you can see the arrow on the video fall out after the bear made about 4 steps. The arrow didn't penetrate the chest cavity, it looked as if it just cut up the hair and then fell out. Now this is not common at all, but it does happen. Also even on perfectly hit bears, I very rarely see a complete pass-through with a expandable. With fixed heads it is uncommon (unless the head gets stuck the opposite shoulder) that we don't get a pass through. Now before I get flamed on here about how you don't need a pass through to kill the animal you are right. However guess which one is easier to track through the thick Canadian bush. Yep the one with a hole on both sides. Also, with a pass through you will get a lower exit hole that will leave an easier to follow blood trail. Loosing an animal does happen with both style of heads (not very often but it does happen), but the large percentage of lost animals comes from an expandable broadhead. These are just my observations that I have experienced. I have about 35 bowhunters a year, so I get to see alot of different setups. Fixed blades are the best in my opinion.
Thanks.
ps....most bear hunters like to shoot a bear like it is a whitetail, as close to the front shoulder as possible. On a bear move it back a little, go from the mid-point of the bear and go forward a bit. If you try to go from the front shoulder and move back you will most of the time hit dangerously close to the front shoulder. And if you hit a good bear in the shoulder....well sorry but the party's over, unless you cut the artery that runs down the front leg, you are out of luck. A bears vitals sit back a bit more than what most people are used to with deer. A good double lund shot is what you are after. A good hit will leave a bear only 30 or so yards from your stand, easy to track, and quite a few hunters get to see the bear go down.

Good Luck on your hunt, and don't be afraid to call or write your outfitter on any questions you may have. Most of us are hunters ourselves (yes there are some that are not) and just love to talk hunting.