I would say it all depends on your experience level. A bosal in my opinion is easier to screw up a horse with if you don't really know how to use it. Just like a snaffle can be very harsh if not used corectly. I think the next horse I start I'm going to give the hackamore( bosal) first a shots and forgo the snaffle. Just to see. The last one I started I started him in a snaffle then moved him to a hackamore and he's getting ready for the two rein. As soon as I get a bosalito for him. That being said I didn't even saddle him until he was 3 and some change. It was a timing thing and seemed to work ok. That's him in my avatar
It really depends on the colt, you have to feel that out. Some horses are better off started in a bosal and some I like to put in a snaffle first. I usually do a couple of rides in a halter and a make a decision from there.
Snaffle...most shows you can't use any bittless bridles in most shows...there's a age limit
You can ride at AQHA shows in a bosal until the horse is 6. Horses are 6 are junior horses and either a bosal or a snaffle is acceptable. Horses 6 and over are senior horses and must be ridden in a shank.