anyway, on topic:
First senior footy = bullsh*t. Make the criteria 5 years residency under the age of 18. If you are eligible for both, you pick the one you feel closest to. If you don't meet the residency criteria by the time you are 18, you shouldn't be playing Origin anyway (this applies to Kiwis who come to QLD at 15 and are suddenly QLDers).
Imo is the best way to both have a fair competition and keep state passion at its maximum. I don't agree with choosing by birth. Wouldn't make sense if someone was born in NSW and then spent the next 20 years of their life bending bananas and was forced to play for NSW.