Not a Preference, But What I Am Using Now
I usually just buy what's on sale. But, currently, I am using A&H with Oxi powder. I love the retro scent: it is not flowery, and reminds one of the old powders way back when such as Cheer, or Tide Intensified.
When washing whites, I put in an extra scoop of Oxi-Clean from a tub I have left over from before the A&H.
After viewing this thread, however, I have taken note of what everyone is using for their darks and blacks. I am not pleased with how mine so quickly and easily fade.