I guess I'm old school. I feed sweet feed (Vitality 10%) and hay, whatever hay I can get that is good, mostly Coastal Bermuda. I also feed Alfalfa cubes, soaked.
The only time my horses have colicked was due to HAY not sweet feed, so I don't know where that idea comes from (as mentioned in an above post). I rarely have horses colic. I think a lot of colic is more management practice than what you are feeding (of course I'm not talking about feeding moldy or bad feed).
Also, I have to wonder, those of you feeding just hay all seem to use vitamin supplements? Why? Why not just include a well balanced feed with the hay?