If the Party pictures are going to be without the flash, you will probably be disappointed in the results.

While the camera makers claim higher ISO settings for those cameras, those higher settings come with a lot of noise.

You should also consider the Fujifilm F20, F30, F31, F40.
Those cameras have the least noise at higher ISO settings than any other small camera. They also have a very strong flash, which can light up a small room.

As far as problems with the Canon SD750 and SD1000, I have not heard of any.
They replaced the SD630 and SD600, which produced a sharper image.
All three of the camera you mentioned are about equal in image quality and sharpness. The older SD630 and SD600 were a bit sharper.

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