Diving in New Zealand

I'm looking for some advice re diving in NZ. I have just been diving in Milford Sound and will be diving in poor knights in 2 weeks. I am returning to the south island in Jan and prob only have time/money for one more dive does anyone have any recommendations on whether I should choose the mikhail lermontov or diving at Stewart Island or possibly a great white shark cage dive at Stewart Island?!

Thanks in advance

Stephen