I have a completely set up tank but at this point I just don’t know what color or type of Betta to get because they are all so pretty. All suggestions are majorly appreciated as I know some Betta types are prone to some diseases and problems.
Now this is the important part. Stare reaaaaaalllly close at each one. With one eye closed, stare right into the fish's eyes. Ignore that other customer giving you a strange look, they don't know how to pick a good fish.
Now just choose the one that speaks to you the most, for whatever reason.
Make sure eyes are nice and clear, no white fuzz on the fins or body, isn't too thin or bloated, should have a nice smooth texture to the scales. Make sure fins are in decent shape... is the fish active or lethargic?
Things to consider looking for a healthier one.
Though, if a pitiful one catches your heart, its up to you to give it a chance of recovery as well, if you are up to a challenge.