I did my BMQ in the fall, and all of the instructors say that combo are better, because that way you can't lose the key.
Having said that, mine were key locks, and I just made sure that at all times I had a spare key in the map pocket of my tac-vest, as a fail safe if I ever locked myself out. If you're going to get them all with the same combo, then combo is cool, but personally I can't keep track of two separate combos.
Another idea that I don't believe was mentioned is a small flashlight with a blue and/or red light filter. You can go hog wild on this, but I made it through my bmq/sq with a $4 one from canadian tire. Again, draw your own conclussions :warstory: