They are all quite similar, except the SD 1100 only has 3 x optical zoom, the others have 4.

They are all just very basic little P&S cameras, with little manual control (i.e.not good for learning about photography). They all have the same limitations which will bother you from time to time (e.g. shutter lag and poor low light performance).

For what it's worth - if I was in the market for a P&S camera right now, my choice would be a Canon Powershot SX10 IS http://www.usa.canon.com/consumer/controller?act=ModelInfoAct&fcategoryid=144&modelid=17630