I've seen all of them mentioned here, loved each one I've seen. Each brought a unique voice to whatever production they were in.
But enough of democracy, I saw Len and as it was written for him, he 'got' the humor, pathos and subtleties of the vocal lines just right. However, it nearly killed his voice as he is more of an actor than singer.
In a few years we will all bring up this debate again, because Depp will surprise us all, I hope.
Like Len, Sondheim always prefers an actor who sings than a singer who acts (Mandy included--even though he doesn't realize always that he's truly an actor). It's more important to get the word and intent across than the notes. The rest will take care of itself.
Ask any composer...
"It's not so much do what you like, as it is that you like what you do." SS
"Time flies like an arrow, fruit flies like a banana." GMarx