1) La Nouba is one of the best shows you'll see. I'm a huge fan of the Cirque du Soleil shows. I've seen La Nouba (5 times), Mystere (4 times), O (1), KA (1), Zumanity (1), and Varekai (1). Next year, when I go back out to Vegas, I'm going to check out Love and La Reve (La Reve is not actually a Cirque du Soleil affiliated show, but it is created by the creator of Mystere).
2) Best seats are about midway up. Someone mentioned behind the sound board... that's where I usually get them. Being down in the 100 level is nice and you do feel as though you are 'part of the action'... however, the Cirque du Soleil show is, for lack of a better term, an assault on your senses.. especially visually. There are things going on all over the stage at the same time (even off to the sides of the stage). The closer you get, the more limited your peripheral vision is, meaning you will miss a lot (I've seen it 5 times and I still catch new things every time) that is happening to the edges of the stage. Also, there are portions of the show that happen in the walkway between the 100 and 200 sections... which means that, should you choose to sit in the 100 section, you have to turn around to see what's going on... whereas, in the 200 section, you're always facing forward.
Avoid the far sides and far back of the theater. While you can still see, it's not as good as being toward the bottom of the 200 level.
3) When you go, take a minute to realize and enjoy the fact that EVERYTHING you are seeing is live and not pre-recorded. Yes, the music is live. Yes, the singing is live. It's all being done for you then and there.
La Nouba is second for me in regards to the Cirque shows. Mystere, in my opinion, is heads and tails the best I have seen of the bunch. However, as far ahead as Mystere is, that's how far ahead I think La Nouba is from the rest. Just an amazing show. I can't really say enough good things about it.