Different areas of the country seem to have different hays available. For instance timothy hay is unavailable here. I like a good prairie hay but if you have pregnant mares you wouldn't want to feed that due to possible fescue types in it. Brome hay is very popular here and I prefer it, but it does seem to put more unwanted weight on. I buy large round bales and keep some small squares for traveling and when the weather is bad and I have to stall. The big round bales wouldn't be advisable for a single horse since it would probably go bad before he got it eatten. When buying hay look for a nice green color, good smell, more leaf than stems and no junk (twigs, weeds). Watch out for mold, I bought 16 large round bales this fall and every one had mold in them
Thank goodness my hay guy replaced them all
but I did have to take prairie hay over the brome. If you want you can have an analysis done, check with your local extension/ag office.