It doesn't matter what you use. It depends on how far along your hrose is when it comes to collection and softness through the poll, jaw, neck and nose. If you work with your horse alot on these things and he is extremely sensitive to it on the bit you use, then it is safe to graduate to a halter or hackamore. Once the horse is sensitized to pressure and willing to obey, there is no need for worry in a halter. Some horses will catch on right away, some may take a couple rides, because the pressure is being applied elsewhere. If your horse is cued with neck-rein and/or leg cues, then the previous sentence may be ignored.
Ya'll keep talking about trust. Some people trust their horses 100% but they have never taught their horses to be soft through the jaw and such. This is also a key role in using a hackamore. If your horse tends to buck or run away with you, no I do not suggest using a hackamore/halter for riding.
Some people have a deep hatred towards bits, which, in reality, and I am sorry, is stupid. The bits are not the problem, it is the people. If an experienced horse-man on a good broke horse (obviously it makes no sense to use such a bit on a green horse) used a "cruel" bit on a horse, he could do extremely well with it. Somebody who is unexperienced and/or riding a horse that is green or ignorant towards the issue of softness all through the poll, jaw, and nose, then I would not recommend use of a harsh bit. A 'Tom Thumb', Ring Snaffle, or any other short-shanked broken mouth piece is always a good way to go.
It is difficult to tell people what bit, saddle, or other equipment to use. It all depends on the rider and horse.