I second
@k.idmnt66, it's really a matter of your operation and what you're trying to do. We'd need a little more information.
But generally, round bales are ideal for large operations and feeding cattle. They're faster to bale, shed water better when stored outside, and let you put up a lot of tonnage with less labor. The main drawbacks are needing a loader to move them and potential waste without the right feeder.
Square bales are great for smaller farms and horse owners. Small squares are easy to handle by hand, store neatly, and sell for a premium, but they're labor-intensive. Large square bales offer the density of rounds while stacking neatly, but they require a bigger tractor and budget.