There are plenty of opinions about which application round is the best one to apply in. The straight answer is that there is certainly an advantage to applying in the first round, but never enough of an edge to make up for an application that is even a few degrees below the best one you are capable of given more time to prepare.
Round 2 in early January is when most applicants apply. While it's a competitive round, consider that admissions offices are now working at full-capacity and are very motivated to fill the class with the best candidates available. They too are competing and now they have a complete picture of the applicant pool they will be drawing from, a position they weren’t in when reviewing application in Round 1. In addition, to the extra time to perfect your application, one of the advantages of applying in Round 2 is that you will have more time for school research, and you will be able to conduct a school visit while classes are in session.
Which brings us to Round 3 (and Round 4 at some schools). Sorry to be the bearer of bad news, but Round 3 is like one of the rings in Dante’s inferno -- a place of heartbreak and eternal suffering. Unless your profile is beyond exceptional and you are one of the luckiest people you know, you would be joining a game that is pretty much already over. Rather than applying in Round 3, our advice is to start working on your applications in the spring but hold off until Round 1 of the following year to apply.