I have fed alfalfa hay, timothy cubes and oat straw in the past.
I found first cut alfalfa preferable for the easy keepers as the stems and stalks are more 'robust' and that slowed down the power eaters abit. The first cut did have some grass in it so I fed at a rate that amounted to, by weight, approximately two thirds of what I would have fed in grass hay. I used second cut (lots of yummy leaf in it) on a hard keeper with dental problems for many years -- only a couple of flakes a day as he had a large pelleted seniors feed ration.
I used timothy cubes to supplement some poor quality hay - that's all that was available that year. I found it interesting that the horses ate the hay first then the cubes. But they got through the winter fine.
I used oat straw to supplement some good hay - good hay was scarce that year but oat straw plentiful. While the hay was rationed, I was quite generous with the oat straw and it was a good winter for the horses. One thing with oat straw that I had been taught was to watch out for frost -- apparently if there is a frost on the crop while it is standing it can 'fix' nitrates in the stalk thus making it toxic for horses; frost is not a concern on straw that is already baled. My sister (the same year as I got mine) was concerned with this as she was about to buy from a different location than mine; she took a sample to the lab for analysis and it was fine.