There are two ATP fixed-wing exams. One is an FAR 135 exam (non-sked mostly) and the other is an FAR 121 exam (scheduled larger airlines). The FAR 121 is "not a joke" to pass. The FAR 135 is probably much easier. Your license will say ATP, regardless of which written is taken. So, take the easier one.
Good luck,
Check 6
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Kick the tires, light the fires, first off is lead, brief on guard.