I use it, it may be a little pricey, but I got a cheap version of Amazon. I recommend getting versions 4, 5 or 6. Don't go before version 4, because it is unlikely to work on Snow Leopard.
MuseScore - is finally a very stable and good release - it wouldn't hurt to give it a try before spending the cash for Finale or Sibelius - I personally own a copy of Finale 2007 which still runs great on Snow Leopard
Yes you can print sheet music in GB. It's limited with editing but it can be done. I would try GB first and to the extent that doesn't suit you then start looking into alternatives.