There is no universal works in all situations anti air. For example, Ferra Thor cant anti air with d2 like liu kang. You should go with your main into the lab to determine which his is best anti air. Also, the effectiveness of your mains best anti air changes depending on the jump in punch animation of your opponent. For example, Kotal, Sonya, Tanya kind of arc their bodies backwards so some anti airs won't work with them so you gotta use others. If you are having issues AA one particular character go into the lab and practice different moves for AA against jump ins and cross overs against that character. Usually the best options for AA are d1, d3, s1, and b1 but that is character dependent. Another thing is that AA in MKX is kind of a read you kind of have to be expecting it and react fast. One missed timed AA will get you hit but if your opponent is being a jumping bean then you can easily predict the jump and punish him.