For me, MEMENTO is the gold standard when it comes to Nolan.
I'm not a big fan of
Memento. In fact, when I first saw it (back in 2000), I liked it for its unique structure only. I've seen it twice since (last time in 2009), and I recognize the genius in it now. But I find little to celebrate in it apart from that narrative. I do like the movie. But don't love it.
I've seen
Insomnia once, never saw it again, I'll give it a watch again though. Apart from
The Following (excellent movie!), it's the only Nolan DVD I don't own.