Yoga or Pilates for Posture
My point of reference will be: affecting change in posture for better alignment.
In terms of efficacy, I'm not sure of the studies put out there, but they both have their merits and it's really just as much about who and where you are doing pilates or yoga with.
I'm going to play devil's advocate (as a yoga teacher) and say that pilates (on the reformer) may provide more consistent results overall, as, to my knowledge, pilates is much more uniform in terms of certifications.
Other considerations are the fact that pilates came out of a rehabilitation and dance tradition so there's a different emphasis, where yoga has a large philosophical side to it.
And then you have to factor in personal sessions vs. group sessions (if it's on the mat).
There are other methods like the Alexander Technique, the Feldenkrais Method, Somatics, and Body Mapping that address posture and alignment in different ways and is used by dancers, actors and musicians among others if you wanted to look into alternatives that don't involve sweating.
