There aree a few minor differences with some breeds/varieties but few & minor are the opeerative words. Generally a bird that places well with an APA judge will also place well with an ABA judge.
One other difference is that the ABA Standard includes quite a few more varieties than the APA Standard as well as some additional breeds.
As to the origional question no breed is better to show than another. The best bird at a show should always win regardless of the breed. However, in some of the more popular breeds quality stock to start with is easier to find. Examples being Cochin Bantamn & Old English Game Bantams. They're very popular with a number of good breeders all over the country. The flip side of that coin is of course, due to their popularity, classes are quite competitive.
I'd advise you attend a couple of shows & look at birds before you make a decision. Aesthetics are a personal thing & what appeals to one person may not appeal to another. It would be best to choose something you'll enjoy looking at every day.
One other note, I believe you mentioned Showgirls in your first post. They are recognized by neither sanctioning body so they can do no better than best of Breed in a show anyway. Besides they're hideous-my aesthetic opinion. Don't care for Silkies either.