Hey RichardinSF,
I stayed at the FS last year. (I didn't bring it up in previous posts because the OP wanted to know about the Observatory and PH.) I liked the FS. I had a corner junior suite. Views were phenomenal! From the room, I could see from the Sydney Bridge, look down on the PH (it's not a judgment -- no flames please) past the Opera House out to the Pacific Ocean. I think the FS was the Regency before.
Also, if the OP wanted to immediate access to the CBD (central business district), you can forget it -- the Observatory is closer than the PH. And that's a walk in itself.
I had dinner one time the PH and the restaurant was WON-DER-FUL! If you don't stay at the PH, then at least eat there. Top notch service, excellent food. I had some seafood appetizer -- a taste everything -- and the Australian etiquette there was a specialized knife and fork for each type of seafood! Wow!
David