Depends what your application is. For general CB and freeband use, the S45 is excellent. Very, very stable, excellent audio, both AM and SSB. It has certain adjustable frequency features that make it versatile. Plus relatively high power, makes it very attractive. The only thing I don't like about it is the 5 digit display. For amateur use, it has full 10M coverage, repeater splits, and an undocumented feature: 88.5Hz subaudible tone.
The advantage of the S9 series is 6-digit display, but unfortunately for amateur use, it doesn't have repeater splits, or subaudible tones. For general CB and freeband use, that isn't a concern.
I'm looking to acquire an S9-175 soon. (I'm also looking at the RCI-Ranger 68FFC2, but that is another thread.)