Awesome show! There really isn't a bad seat in the house - the theater is "in the round." However, I suggest sitting farther back, the closer seats are in the splash zone. There is also so much going on, sitting back a bit allows you to see it all.
If you're willing to splurge, I really suggest sitting in the Champagne Circle. You have private seats, with a TV that shows behind the scenes and under water action. You also get a bottle if Perrier Jouet and a selection of chocolates, truffles and chocolate covered strawberries.
Le Reve is one of the best shows in town and definitely worth seeing. The performers are all incredibly talented and you won't be disappointed!