Ok, appellate stats nerds, time to rejoice!
The 2015 reports are available now, here, appellate report here.
The Ninth Circuit remains the "busiest" by far, with over 12,500 cases commenced in 2014. By way of comparison, the next busiest Circuit is the 4th with about 7,650 cases. And the Ninth is also the slowest in setting argument (or submitting w/o argument): From the Appellee's last brief to oral argument or submission (in civil appeals) is a median of 15.4 months. (The 8th Cir. is the second slowest, at 5.1 months.)
The nationwide statistical reversal rate in private civil appeals is 12.4% -- but the figure is 19.2% in the Ninth. (Yes, that's the highest; the second highest is the 7th Circuit, at 18%.)
One area in which the Ninth Circuit does not lead is in the percentage of unpublished decisions: The Ninth is only at 91.5%, but the 4th (93.8%), 3d (92.8%), and 11th (92.4%) are all higher. The D.C. Circuit is by far the most likely place to get a published opinion, with an unpub'd percentage of only 50.5%. Another area where the Ninth is not at (or near) the fore, is in cert petitions granted. It seems like if you want to get to SCOTUS, you should be practicing in the 11th Circuit.
If you're a nerd of the more typical sort, but still a lawyer, then this (here) would've been your dream assignment!