There is effectively NO difference between Rounds 1 and 2 for schools that have 3 rounds or more.
Some folks prefer Round 1 because they have the time during the late summer to really crank through the applications in time for Oct deadlines (and want to avoid working on apps during Thanksgiving/Christmas). And others prefer Round 2 because it's only that time between Thanksgiving/Christmas when they have the time to work on the applications. And some folks decide to spread their schools across both rounds - a few schools in Round 1, and then a few in Round 2.
Apply when you're ready. You're better off putting in your strongest effort for Round 2 than a rushed effort for Round 1.
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