Vandy v Pitt is a good problem to have.
Full disclosure is that I'm profoundly biased toward UPMC, but both are, in my opinion, excellent training programs.
I interviewed at Vanderbilt and loved it. It was very high in my rank list; I was especially impressed with the intern year (which seems to be a MUCH more "aggressive" year than the CBY at UPMC) and the anesthesiology presence in the ICU. Vandy Valet is a stroke of genius, too, and I wish we had something like that here.
UPMC was my top choice, and where I ended up. I'm very, very happy here. Closer to home, and I grew up a Penguins fan, too. More importantly, I did not find a program with a better total training package than UPMC, in terms of volume of cases, educational balance (intraop/lecture/simulation/etc), subspecialty exposure, and happy residents. As a CA2, it seems like I "bought what I was sold" - the things you were told about on your interview day, and by the residents at the dinner beforehand, are the things you get when you're here. And the program really does seem to care. We (residents) are invited to the annual residency review retreat that the faculty & Chairman attend to discuss/improve the program, and real changes come as a result of our input. It's a big place, but you tend to work with a finite faculty so that they do know you by name after not too long.
UPMC is not perfect. I am on call, wearing an ID holder than contains the badges for the 7 hospitals I've rotated at thus far. 7 different ways to square narcs, 7 different things to do before bringing a patient to the PACU. It's good for me (now), but I *hated* that at the start, since every month or two brought a new way to do the same thing. If you want to settle in and plant roots, this might not be the place for you - although it does make you very comfortable at adapting when the circulator says "We don't do it that way here" minutes before your case starts, or if you're missing your favorite drug/blade/etc. And I wish I'd done more fiberoptic intubations by now.
Overall, you cannot go wrong at either place. I really am very, very happy at UPMC, but would likely have been thrilled with the Vandy experience, too. Let me know if you have any specific UPMC questions.
...and good luck with the Match!