Well apparmor is like the baby cousin to selinux, or the big brother to the traditional unix DAC. Selinux is more robust but also more complex. Grsec is an attempt at both a MAC and various exploit-prevention techniques. In that sense, grsec will be more effective at preventing "traditional" exploit techniques.

But modern software development is so bad, even after using high-level languages and abstractions, much of the webapp and backend development is rife with security holes. You don't need to use things like buffer overflows anymore to simply extract data or take over accounts. Servers are so easily accessible and botnets are so widespread that owning a server isn't really the point anymore; once you have all their data, who needs root?