I do think BeOS is quite a lovely architecture (not sure how faithful Haiku is to BeOS deep down, but it appears to be close), and I used BeOS PE5 for about a year in 2000/2001... But we have to be honest, in 1996 NeXTStep was far far more mature than BeOS.
Maybe with the 5 years of development that OSX received between 1996 and 2001, BeOS might have been brought upto spec... But I think given the state of both operating systems, Apple made the right choice... The thing I'm most impressed about OSX/iOS and it's developer environment, is the maturity of the whole thing, it feels so solid and carefully thought out I've never felt so comfortable :-/
