Of what I've seen, in order (best first):
1. Ave Q
2. Dirty Rotten Scoundrels
3. Wicked
4. 700 Sundays
5. Monty Python's Spamalot
I've also seen (of whats currently on Broadway, and still, best to not as best (IMO)
Twelve Angry Men
All Shook Up
Mamma Mia!
The Producers
Rent
Little Women
La Cage aux Folles
Hairspray
Chicago
The Phantom of the Opera
Dame Edna:Back With A Vengeance
Fiddler on the Roof
Good Vibrations
Beauty and the Beast
Brooklyn the Musical
Have tickets to (but haven't seen yet):
Chitty Chitty Bang Bang (tomorrow night)
Pillowman (April 16)
Sweet Charity (April 18 with Ms. Applegate)
Lennon (July
A Streetcar Named Desire (I forget when)
Of course it matters who is going. If it's ten year olds, Beauty and the Beast moves to the top (probably Chitty and Lion King up there too). I can't really comment on any I haven't seen yet, but have heard/read good things about Doubt and The 25th Annual Putnam County Spelling Bee. Of course, all of this is just my opinion after seeing them.