million5:
Generally speaking, the earlier rounds for most MBA/masters programs are easier because there are more seats set aside for admission. There's a common understanding that rounds 1 and 2 admit about the same percentage. Sometimes a round 3 is included in that grouping if there are a total of 4 rounds in the program's process.
The rule of thumb is to apply in the earlier rounds but apply in the round you are most ready. Do not rush your application for round 1 simply to get it in before round 2. The quality of application matters.
Of course, you should check with the specific schools to which you are applying to understand how many rounds they have and if the admissions office is offering any public feedback on which rounds may have a higher admission.
Also, not sure if this is relevant for you, but international applicants have to apply in the earlier rounds for visa and other related purposes.
Let us know if you have any other questions.