What bags do you think have the nicest, softest leather?

Although not all Rebecca Minkoff leathers are soft - but her Black Cat leather is some of the softest, most supple leather I've ever seen in that price range - its the only bag I've ever owned that made even my DH comment on its softness. Also, Belen Echandia's Matte Chocolate leather, once it is broken in - rivals Balenciaga in terms of drape and silkiness (however, this can take a good long while - so I'm not sure its a true candidate).

Some of Valentino's pleated bags also have similar leather - thin, very soft, and supple. Same with Prada.

Its hard to say overall, because most brands use different leathers from style to style and from color to color.