I gotta say, during the vanilla i played mostly Hellfire Scorpion and Ninjutsu, only when his double flame aura got nerfed and ninjutsu got buffed along with Hat Trick the second time, is where i started to play hellfire less because i felt he lost an essential part that connected me to that variation.
Ninjutsu on the other hand after the buff i felt way more comfort using it since the lack of damage was basically inexist after that patch where the scale of B2 got reduced.
In fact i don't think i ever switched mains, i just added little by little as i came to understand them or according to the needs of the meta.
Scorpion (Hellfire/Ninjutsu)
Kung lao (Hat Trick)
Tanya (Naginata/ Pyro)
That's pretty much it, if i tell you, i played predator or other character that are not these and felt comfortable with them i would be lying.
I tried Cassie, Johnny Cage, Sonya, Predator, Kenshi, Kung Jin, Reptile, Kano, Kotal, but didn't really shared a connection with the rest so i ended up dropping them.
Even Sonya who was easy to play.