Here are a few of my personal choices for determining a quality show betta.
You cannot get much better than this for a Doubletail Halfmoon caudal. Nice even lobes that have a strong 180 spread that are clean cut. This photo was taken when he was younger but his finnage has grown in a little more and now they all lay together very nicely to make a arc without any bumps or edges. On a double tail it is common to have a short, stocky body so make sure you breed them to a girl who is long backed.
Good even symmetry throughout all fins and a strong dorsal base which is half the length of his topline. Notice the thick body and smooth
This is a new boy I will be receiving soon, I just thought I would put this right next to his picture so you can see the similarities.
A few things would need to be tidied up such as strengthening the first ray of the dorsal so it is longer and then sharpen the anal point a smidgen more. But he has the ideal caudal, body shape and thickness and his overall symmetry for a asymmetrical HMPK is near perfect.
The girl he will be bred to.
I thought this would be good to put in so you not only see a good show specimen, but know what to get for the partner in order to compliment the stock you have. This girl has an awesome dorsal, wide base and shape with the rays I need to make the dorsal point forward with a longer ray. This picture does not show it well but her caudal is a strong D shape I would prefer sharpers edges, that is where the boy's caudal comes in. Her anal is level and has a good shape to it. Her topline and body thickness could be improved, once again why the boy compliments her like a glove.