I had a breeder tell me once that all classes other than OPEN are a sure sign that you do not think you dog is good enough to win . She called them all "the I don't want to win classes".
Does this hold any truth? I would think that if a breeder had a nice young dog entering in Bred-by would be a good thing.
How do you think your dog is maturing? If it looks older and more mature - then enter Bred-By (if you are the breeder), or Open. If it is nervous or you are a new handler - try Novice a couple of times. The only problem with Novice is that there usually is no competition. I think Am-Bred can be very competitive - if you are comfortable in the ring - go for Am Bred.. Depends on the dog and the judge you are showing to.