What is the difference between the Canon PowerShot SD980 IS and Canon PowerShot SD940 IS and Canon PowerShot SD780 IS ?

Which one is better?

- Canon SD780is : 12.1 MP , 3x zoom and 2.5" LCD

http://www.amazon.com/gp/redirect.html?ie=UTF8&location=http%3A%2F%2Fwww.amazon.com%2Fs%3Fie%3DUTF8%26ref_%3Dnb%255Fss%26field-keywords%3Dsd780%26url%3Dsearch-alias%253Delectronics&tag=computer0bd-20&linkCode=ur2&camp=1789&creative=390957

– Canon SD940is : 12.1 MP , 4x zoom and 2.7" LCD. It offers better zoom, bigger LCD, updated menus, and stronger performance

http://www.amazon.com/gp/redirect.html?ie=UTF8&location=http%3A%2F%2Fwww.amazon.com%2Fs%3Fie%3DUTF8%26ref_%3Dnb%255Fss%26field-keywords%3Dsd940%26url%3Dsearch-alias%253Delectronics&tag=computer0bd-20&linkCode=ur2&camp=1789&creative=390957

– Canon SD980is : 12 MP, 5x zoom and 3" LCD. Better zoom, bigger and come with touch-panel LCD

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