As far as I know, JRB's score is MUCH MORE complicated than Sondheim...
Erm, well, first JRB only has three shows, one of which is a song cycle. His shows are complicated, sure, but I'm not sure if they are as masterfully crafted as Sondheim.
He's great though, and I'd like to see more from him.
It's true, LaChiusa might never have a hit, but he's not trying to make a hit, he's trying to write a really good show. His subjects for musicalization are a THOUSAND times more interesting than Wedding Singer or Mamma Mia could hope to be.
He's a brilliant man, who might never has his full due, at least not in the near future.
Yazbeck will be fine. He's a great writer for the theatre, if his songs can become a bit repetitive. And he chooses smart material, while not particularly deep or off beat, that are always well written.
I think Tesori will straddle the line between artsy shows like Caroline and Violet and big musicals like Millie, and Shrek.
Guettel's rich, and takes his sweet time writing things, but I have a feeling that Princes Bride will be even more a breakout hit than Piazza. Great source material, and I have complete faith that he will write a fitting score that integrates the intelligence and very specific humor of the film, while being incredibly inventive.
Personally, I think I have too much bloom.