Given that getting an interview will take a while, I’d have him start on L-1B while completing NVC process and then go back to Nigeria for interview when scheduled. Doing AOS which strands him until AP, EAD for months and could take years makes no sense.
Arriving on immigrant visa is superior as it starts his permanent residency at POE and he has naturalization in sight 3 yrs later vs waiting 1-2 years for residency THEN starting the clock for naturalization in 3 years.