My guess is Amazon - they're involved in enough different lines of business that even if one drops off, they'll still be fine, and if all lines of business prosper, they're in for huge growth.

E-commerce should continue to drive huge revenues, their cloud offerings are supporting a lot of emerging companies and technologies (which hopefully continues), and if they continue physical product offerings (semi-transformational things like the Kindle), they're looking good.

as an aside it'll be interesting to see what social sites do long term - perhaps Palantir's focus on brilliant engineers and consistent growth will let it eclipse Facebook/Twitter/etc at some point?