The near ideal version to have is the one on Decca with Barbara Bonney (in top form) and Andreas Scholl if you don't mind having a counter-tenor for the alto part. I'm personally a fan of Scholl so I'm biased. I heard his recital at Davies and it was one of my most memorable concerts. Back to the Stabat Mater, the Decca version also benefits from Christophe Rousset and Les Talents Lyriques. The orchestral sound is nicely layered.
Your final decision may depend on the coupling.
