I think you are going to find a lot of varied answers to your question as many Forum members feed as many different feeds as there are members!
This is what works for me:
Weaned foals -
Progressive Nutritions Alfalfa Diet Balancer, Progressive's Foal Starter and Creep Pellets, Alfalfa pellets mixed with some beet pulp, Alfalfa hay and grass hay.
Broodmares and stallions - Progressives' Alfalfa Diet Balancer, alfalfa pellets with some beet pulp, grass hay.
Mares with nursing foals - same as the broodmares with added Progressive Foal Starter and Creep.
Yearlings and 2 Yr olds - Same as the Broodmares and Stallions, the only difference is the amount they get.
Show horses -
Progressives' Alfalfa Balancer mixed with Progressives High Fat balancer as needed, dry beet pulp, alfalfa pellets and grass hay.
Any horse needing more weight can have Progressives High Fat Balancer, more alfalfa and more beet pulp.
Any horse needing to lose weight can be fed Progressives' Grass Formula Diet Balancer and grass hay.
I don't feed any grain here and have been very successful with the weight and condition of my horses with the Progressive products.