There's only A5 Wagyu and so A5 Wagyu is the better since there is only A5 Wagyu.
The A is for yield and 5 for maximum marbling quality and A9 in Wagyu is just a marketing term and sometimes confusion with Australian Wagyu's BMS or Beef Marbling Score 9, which is very high, but not an official Japanese grade, so A5 is the peak quality you can get for Japanese beef.
The kind of cow that has Wagyu meat is the Japanese cow.
The word Wagyu means Japanese Cow.
The most common Japanese cow or Wagyu is the Japanese black cow, the Japanese brown cow, the Japanese shorthorn cow and the Japanese Polled cow breeds, which are known for their intense intramuscular fat or marbling that gives Wagyu a buttery and tender texture
The 4 Wagyu cow breeds include.
Japanese Black (Kuroge Washu) which is the dominant breed, making up about 90% of Wagyu, prized for its exceptional marbling.
Japanese Brown (Akage Washu/Akaushi) which is a leaner, less marbled breed with a mild flavor, raised in southern Japan.
Japanese Shorthorn (Nihon Tankaku Washu) which is a rare breed of cow from northern Japan, making up less than 1% of Wagyu.
Japanese Polled (Mukaku Washu) is another rare breed, found mainly in Yamaguchi Prefecture.
Marbling in the Wagyu meat is the defining feature of Wagyu meat, which is where the fat runs through muscle and creates tenderness.
Unique genetics also promote higher fat content and a lower melting point for the fat.
And Japanese cows or Wagyu are also often raised in low stressed environments with specialized diets to enhance the marbling.
Wagyu cattle were introduced to the United States in the 1980s, which lead to American Wagyu which can be purebred or crossbred, (50% to 100% Wagyu genetics.