selinux is a bit (over)complicated - both in model and in usage (it doesn't mean that those are not needed - it only means that some of them are not needed by majority).
grsec offers same features as selinux (well, at least most of them), but implemented (and managed) in different way.
To use selinux you need a lot of experience and understanding, while grsec can be used by novices in (more or less) intuitive way (there are some problems too, but not as much as in case of selinux).
I just had a look at selinux - and I see that it will take few days to learn how to use it efficiently (and correctly), and few more days to tune it up (for specific systems).
There is one definitely good point for selinux - it is in mainstream kernel (2.6), and is officially supported. Those guys from NSA have a lot of experience (and very good team) OTOH, some people scared to use NSA's Linux... So...
My advice - try to read all relevant docs, and see what fits your needs better - both from features and management (usage).