I also prefer Pacific to BOB, but it's not a landslide. They are both exceptional, amazing series. One thing I
liked better about Pacific was its final episode, I like how they spent more time on their return to civilian life, and actually followed them back home to the states to emphasize the difficulties in that adjustment rather than just wrap things up with a voice over epilogue. They closed out the series with a little more impact that way.
I also thought Pacific better depicted the significant impact that war violence can really have on a man, and change him and force him to endure some pretty intense emotional struggles. BOB touched on this, but Pacific drove it home more viscerally. One reason is simply the subject matter, the Pacific theater was far more consistently and pervasively brutal than the European theater.