Both cameras have the important manual controls.
The S90 uses the larger sensor and bright f/2.0 lens to improve its low light performance.
So, if you plan on using the camera in low light situations (without flash), the S90 is the better choice.
If you have need of more optical zoom, the SX120 is the better choice.
I have it narrowed down to either the S90 or the SX120. Which would be a better camera for me? Would the S90 be too much camera for me? I realize it's double in cost, but want to get the best pics. I do like the zoom on the 120 though. But if I understand things correctly a bigger sensor size is better and the S90 has a bigger sensor. I won't do much with manual, but may on occassion. I will mostly be shooting family pics and vacations. Thank you!