For me, round bales are cheaper - saves me about $700 per horse per year. Also much less work - putting in a new bale once every 2 weeks instead of filling hay racks twice a day. Not to mention I don't have to stack square bales in the 100 degree loft while hunched over because it's too short to be able to stand in. I don't miss that! I keep my round bale inside the run in so I don't have to worry about rain.
My horses are more content with 24/7 access to forage, and it's better for their guts, too. Horses evolved as grazing animals so their gut is best suited to be eating small meals throughout the day. They don't do well without something to munch on. When I fed flakes from squares, my horses would suck it down within 4 hours, then spend the next 8 hours hungry/whinnying/eating my fence. Slow feed hay nets didn't slow them down enough. However 24/7 access to hay fixed the problem, and I noticed a significant difference in their attitudes. Yes, they do eat more since they are unrestricted - so I buy lower quality hay. Not moldy or weedy, just more mature, less leafy. My easy keeper does great on free choice mature hay and a forage balancer pellet. I supplement my hard keeper's forage ration with a few flakes of high quality grass hay or grass/alfalfa mix in the winter when there's no pasture.