Pros
I have been at Twitter for about a year and a half and it's been awesome. I've been afforded increasing professional development opportunities over the course of my time, and have been consistently impressed by the awesome benefits - no accrued vacation, great healthcare etc, lots of visiting VIPs and more. The culture is also great. Twitter has done a good job of maintaining a startup-eque vibe despite being 3000+ people. That really comes across in the day-to-day: having random conversations over lunch, or at the themed happy hours where people are super friendly and welcoming. Transparency is also important and respected. In my opinion, Twitter has a really bright future and it's an exciting time to be at the company.
Cons
Nothing comes to mind at this time