I have all three sets. . .I like the Gillespie least, but it's not the strongest Diz material, and I'm a big fan of early jazz so the Bix is wonderful for me (I have almost all the material elsewhere as well). The Pres set. . . I'll reach for it much more often than the Diz (and I have all the material previouslly released on this one as well, and love how here it is all together in uniformly wonderful sound.
My next Mosaic is the OP Trio one, then the Akiyosha-Tabackin Orchestra one. I have all the in print sets.