I would pass on both of those cameras.
Neither one has optical image stabilization.

Very small cameras need optical image stabilization.
Small cameras are difficult to hold steady due to their small size and low weight.

If I had to pick one over the other, I would go with the Nikon.
The Sony W320 is a stripped down model, to achieve a low price line,
and it uses an extra thin battery which will reduce the number of shots per charge.

Take a look at the Canon SD1300.

Here is a comparison of specifications:

http://www.dpreview.com/reviews/compare_post.asp?method=sidebyside&cameras=canon_sd1300is%2Cnikon_cps4000%2Csony_dscw320&show=all

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