For the smaller breeder, I think private treaty is definitely the way to go. Especially since it is so easy these days to get exposure to a LOT of buyers on the internet for nothing, or next to nothing. We put our first bull to ever sell in a local sale this spring. We knew we would probably take a hit on him, and we did, but it was worth it to us to get our name out there locally. We had about 25 business cards on his stall, and by the time he sold there were only about 3 left. That 10% commission sure takes a chunk out of your profit though.
Craigslist is very good, but we got a LOT of tirekickers. That's just something you have to be prepared for posting on a place like that. We have had VERY good success on Cattlerange.com. Most of the people on there are REAL cattle people, and I would say more serious buyers when they contact you.