Kung Jin is really good and I think you'd be pleasantly surprised at how unpredictable he can be compared to Liu Kang and Kenshi because he can throw in a low or overhead in almost any situation. He is a space control character with sweet pressure because of his range, Shaolin is better at controlling the far range while Bojutsu is strong up close. I don't recommend Ancestral, it seems to lack heavily.
People say Kung Jin is easy because he can hit confirm very smoothly with Bojutsu (most people play Bojutsu) either with the bow swing or dive kick. His execution can be a little difficult online if you're doing optimal combos but for 2-4% less damage you can make them really easy. Off any launcher just do a divekick, b2,1-special (bo spin if Bojutsu). Landed a neutral jump punch? Do a dive kick then b2,1,special. Landed bo swing? Same thing. The timing is fairly paced as well.
Most people would agree his best variation is Bojutsu because of the armored launcher and much higher damage than the other two variations.