It changes from game to game, also it depends if it's about design or gameplay, for example i like Chun, Cammy, Guile, Gief, and Sagat as character design but never played those characters much. So for each game characters that i used the most:
3- Fei Long
SF Alpha: (barely play it)
SF5: Start with Laura and Nash, then when Boxer came out it was Laura and Boxer all the way until... Poison came out, and since then it's Poison only
Just not as viable anymore compared to the other characters in the game. The start-up on the fireball is super slow compared to yesteryear. And lastly, dp isn't invincible (Well, non EX dp). I know a lot of people soured on using him since they got rid of that, lol.