I won't feed a commercially prepared horse feed, pelleted or textured. Most horse feeds have ingredients in them that are not good for horses, such as corn, wheat middlings, sweepings, "grain by-products," molasses, etc. None of these things have real nutritional value to the horse and they can be harmful.
A horse's gut is designed to digest low protein, high fiber forage. The closer you stick to that, the healthier and better off your horse will be. A study in the mid 2000's discovered that nearly 80% of show horses (shown at 6 or more shows a year) had some form of ulcers... These ulcers were thought to be caused by a combination of stress, stall confinement, concentrated feed, and not enough long stem fiber in their diet.
So, I make my own feed (plus I feed free choice quality grass/bermuda hay). I get a custom blended vitamin/mineral supplement from Uckele Equine (they have "off the shelf" products too) and mix that with 1-3 lbs of alfalfa or timothy hay pellets (depending on the horse), a little chopped alfalfa hay (I have a couple that choke on pellets), and 1/2 cup of flax meal. Since going this "all natural" route, my horses have showed tremendous improvements in overal health, attitude, and condition. My hard keepers need 1/3rd the food they used to, my girls are easier to handle during their heats, and my "hyper" horses are a lot calmer. My feed bill also went WAY down!
IF I were to look for a traditional horse feed, I would want one with none of the questionable ingredients I listed above. I would want to see feeding recommendations of 2-5 lbs of feed a day for a 1,000 lb horse in light work. I would also talk to the feed company to make sure that they use a FIXED formula and all feed ingredients are grown and processed in the USA or Canada. I want to make sure my horse is not eating anything imported from China, and NO GMO soy products.