I know many factors can make a difference but I'm looking for a simple answer if its possible.
I wish I could tell you there WAS a simple answer, but in all honesty, cannot. Unfortunately the ONLY way to tell what's aboslutely going on with your hay (or grass) from a nutritional standpoint in terms of protein, sugar, starch, and minerals, is to have an analysis done by a forage laboratory. The outward appearance of the hay, NOR THE TYPE, are able to provide that important info. In absence of analysis, all we have to go by is "averages", that is, ON AVERAGE, this hay tends to be lower in sugar/starch/protein than another, but averages will NOT tell you the true story about what is going on with the hay you are providing your horses. Dairy One, a forage laboratory that does wet chemistry on hay samples, has a lot of information on nutritional profiles of different hays they've tested. You might want to visit their web site:
Dairy One -- hay analysis
You may find that alfalfa hay gets a bad rap which isn't 100% deserved. Many grass hays can be higher in sugar and starch than alfalfa and fresh grass in growth phase can have as much protein or more than alfalfa. On AVERAGE, coastal bermuda is generally considered lower in sugar/starch than other hays. Orchard grass can be a very sweet, sugary, high calorie hay. Timothy often times runs right in the middle between orchard and coastal. Mineral content will vary wildly according to where the hay was grown, how it was fertilized, etc. Protein values will vary immensely as well, depending on type of hay and growth stage.
Again, I must emphasize: There is NO WAY to read a hay's nutrition value by just looking at it, so NO WAY to tell if your horse will get more calories from one hay or another. Probably the easiest thing to do is re-evaluate the AMOUNT of hay (and/or other feed items) you are providing. Easy keepers might be able to do well on 1-1.5% of ideal body weight in hay per day (2-3 lbs for the average adult mini), while hard keepers/hard workers may be able to eat hay of any type all day and still not maintain their weight without the addition of extra feed.
Most maintenance adult minis will do fine on a grass hay or mixed primarily grass with some alfalfa hay, or even just decent grass pasture along with a good mineral supplement to fill in any gaps the grass or hay misses. Growing horses, broodmares in late gestation/early nursing, and hard working horses have different requiremenets and feed should be adjusted to meet those special needs. Unfortunately there is no "one-size-fits-all" program for either feed or hay.
Robin C