The easiest anit air moves in my opinion are...
1.) Standing HK very simple and effective. Leaves almost no room for being hit. Uppercut is about as easy.
2.) Back up or run under and sweep. A little bit more challenging since you have to commit to running under.
3.) Back up or run under roundhouse kick. My personal favorite since it leaves barely any room to be hit and with the right character can result in a huge counter.
4.) Air Throw. Easier with Robot Smoke then Jax then Kano then Smoke/Scorpion.
5.) HP. Granted, I use aaHP all of the time, but I believe that it is very difficult for someone to counter if they are not used to doing so. Kabal has the most ridiculous HP I have encountered and can HP spin so easily it is childs play. Robot Smoke is also very easy for me to HP, TP, HP or JK, Spear, Invis, Combo.
Robot smoke in general is basically an anti air character. His Air Throw can be linked with a JK before for big damage. If he jumps back you can get a free TP for 50% plus. His uppercut is very good.