Applying in Round 1 is a good idea if you have a high GMAT score, have engaged your recommenders, and are confident that you will be able to create a solid application before the deadline.
Round 2 is most suitable for students who don't have compelling applications until the round 1 deadline.
Round 3 is the most competitive one. Business schools only have a few seats left and will only offer you one if your application is extraordinary. As a result, it is recommended to avoid applying in round 3. At this point, the schools are looking to admit a particular group of people.