From your list of three, I would favor the Canon SD450.

The other two cameras do not have a viewfinder in addition to the LCD. Most LCDisplays are hard to see in the bright sunlight. Many times you need to revert to the viewfinder.

The Nikon L3 has been reviewed and it has a very long shutter lag (the time it takes to focus and capture the photo). I would avoid it.

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