I've gotten awesome and terrible batches of hay from just about every place I've bought it from, including kms' and Oxbow. For a few years I use to buy exclusively Oxbow but I got so many bad shipments of it that I eventually stopped buying it.
It's kind of the nature of the beast with hay that it's a variable product. There are so many factors that can go towards determining the quality of each batch, things like the weather, how it was stored, how it was shipped, etc, etc.
I think to find the best hay, that would probably require buying it from somewhere local where you can actually go and look at the hay and judge it for yourself. When you order online you can't do that so you kind of just have to hope for the best. Sometimes you'll luck out and get amazing hay, other times you may be disappointed.
With that being said, KMS hay is generally good. My bunnies love their 3rd cut hay. I'd buy it for them more often but I normally buy hay in bulk and to have it shipped to me from KMS is pretty expensive. I usually go with a supplier closer to where I live, to save on shipping costs.