Pivotal is pretty awesome, definitely on my list of "seems cool, bro" companies. A lot of the criticisms I've heard hardly are a concern for me because everything I've known is that they're so busy coding they're hardly able to mess around taking submissions from others outside the company.

And to be a little cheeky, Pivotal (compared to Pivotal Labs, not the same but still) is nowhere near a "start-up" company by most definitions. They're planning for an IPO and are pulling in many millions in revenue like Cloudera and HortonWorks, it's hardly possible to keep these plans from being kept under wraps.

Pair programming is not for everyone. More generally, you want to be somewhere you can learn from senior folk. Pair programming and high quality code reviews are both great for this, and will appeal to different people.