SA3 is your choice if you want to play Yun optimally. it's only real weakness is that it deals small damage compared to other supers. 3 shortish bars allows liberate access to supers and ex moves, it has great range meaning you can combo consistently and use to punish whiffs from midscreen, good corner carry and allows for oki afterwards. Sourai Rengeki would likely be Yun's first choice if Genei Jin wasn't so dominant. It's main weaknesses are in that it's range is limited (so it may drop at the further ranges of cr.mk) and that it offers a single, long bar having you committing to building the super and limiting use of ex moves.
It deals high damage and allows for juggle followups afterwards, allowing for better positioning and damage as well as building some of the meter back. You Hou is very fast super, naturally meaning it can be comboed into easily. Even without Genei Jin activate, he still has some powerful tools but with it his abilities skyrocket and he can take control of the game in a flash. His conversion capabilities are notable too, getting good damage even from light attacks. His offense is quite strong, giving him access to solid mixup game of variable timings to throw off parries and a command grab that allows conversions afterwards. He also touts some potent mobility tools in a fast superjump, variable divekicks, fast walkspeed. With the best super in the game under his belt, Yun is a force to be reckoned with. He first appears in Street Fighter III: New Generation.
Compared to his cocky younger brother, Yun is much more playful and easygoing. Hailing from Hong Kong, he's an upbeat skateboarder and the older twin brother of Yang. Yun is a skilled martial artist of Chinese Kung Fu.