Franzeskaner is excellent.
Paulaner is definitely my second favorite German Hefe.
But the #1 is definitely Weihenstephaner Hefe. Their Lager is fucking great too. It's the oldest brewery in the world (almost 1000 years) and it's the official brewery of the state of Bavaria. The Bavarians do not fuck around when it comes to beer.
The Brothers on Beer Advocate gave it a perfect score and the user reviews are almost perfect.
http://beeradvocate.com/beer/profile/252/731
The only negative is that I've gotten quite a few skunky bottles because it's not very popular and it sits too long.
If you're in Vegas and want really fresh excellent German Hefe, the Hofbrauhaus has their kegs flown in from Munich.
EDIT- While I was writing this, someone posted Weihenstephaner Kristallweissbier. That's very good, but IMO the Hefeweissbier is way better.