There is little difference between any of the Canon SD series of cameras.
They usually differ in focal length (wide or normal angle) or viewfinder (or not),
Here is a comparison of the three cameras you mentioned.
http://www.dpreview.com/reviews/compare_post.asp?method=sidebyside&cameras=canon_sd780is%2Ccanon_sd940is%2Ccanon_sd1200is&show=all
Im leaning toward Canon models SD780/940/1200. Any suggestions.

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