ooh, boy that's a loaded question. Ask 100 horsemen, and your likely to get 100 different answers as to what the best feed is.
What are you looking to do with your minis? How old are they? What they need and what is best for them; will depend on what they are doing, the quality of the forage they are getting and how old they are (just to start, it can get much more detailed).
Many don't need more than a good vit/min supplement, good hay/pasture, salt and water.