Personally, I believe the NZNBL is better, opinions differ, I think Shane Heal came out recently and said the NZNBL is better.
I say that because the imports create better quality, and especially in World Cup years you see all the local Tall Blacks come and play, so you can have teams with a Tait and Webster back-court, and teams having guys like Brian Conklin, Corin Henry as well as ex-NBL imports like Braswell, Devendorf.
I'm no SEABL expert but the end-of-the-bench guys are probably better over there, while in NZ it's more top-heavy and you go 6/7 deep of legitimately decent players.
Just my opinion though, sure some others disagree.
Does anyone know if the SEABL has had many former or later-in-life NBA players play in the league? Could be an random, yet interesting comparision