It really depends on if the horse is easily intimidated or headstrong. I've worked with horses of both types, both can be ridden properly with a halter + leads but you just have to do things a bit differently :) Horses that are intimidated easily need more leg cues, horses that are headstrong may need some stronger pulls and possibly a light jiggle of the end of the leads. Riding with a halter and leads is basically different from riding with a bridle only because you have to use your arms differently for it to be a bit more effective, you usually have to pull your arms out to the side more so their head turns, whereas on a bit and bridle you would tug the reins straight back. Riding with a halter is usually more eventful if you are looking for some excitement in life, or just a change in things. Some horses resent changes, it all depends on the horse like most other things.