I work at UPMC Enterprises. During my time so far I have not met a single engineer that I felt I couldn't learn something from. All of the teams that I've come in contact with have good cohesion and little politics. My manager encourages me to take full advantage of my benefits and have good work-life balance.
Cons
They can be slow to recognize and promote key people.
Every person that I've met on my team and the other surrounding it have been excellent. I haven't met anyone that I've felt I can't learn from. There is also a fair amount of flexibility within UPMC Enterprises in the event that you want to try a different role or you want to join a team with an opening. There are also great benefits (and cheap!) due to be attached to UPMC.
Cons
While I understand that security is a paramount concern due to handling patient data in a HIPAA-compliant way, there is an intense amount of bureaucracy surrounding the escalation of privileges. As a developer I can end up spending multiple workdays waiting for access to systems that I need.