A series - The A series is best for you if you're looking for a low cost camera that gives you a wide range of features, many manual controls and great image quality. Although, the size is bigger than SD series making it a jacket-pocket camera, the advantage is in the styling. It gives you a convenient grip on the side which helps hold the camera steady and results in less "blurry" pictures. The mode selector dial on top helps you zip through selections. The convenience of AA batteries which are available in every corner of the world, no missing out on pictures as your battery was discharged, might be a selling point for those who travel a lot.
The S3 IS has a great image sensor, the wonderful image stabilization, a great zoom and super macro function that can produce never before pictures. The flip out screen helps take shots from angles you've never considered before. It's also just a little more expensive and pretty bulky. If taking great pictures is all you care about and do not mind carrying a bulkier camera, the S3 will be a great choice. It's the first step towards a real professional camera.
And finally (drumroll) - the SD series. Small. Cute. Slips into your shirt front pocket without making it sag. If you're wondering about the style, the square "retro" design is better. Does not slip out from your fingers as easily as the curved edge ones. Since it is so small some features like different shooting modes are accessible only through the menu which makes changing between them more cumbersome. Sometimes I've just preferred to stay on Auto rather than missing the shot while I navigated to the right mode. They also have less manual or user defined controls like flash power reduction which I miss. The flash incidentally, can get very strong in lower light or indoor situations and often bleaches out color from people's faces. If you turn off the flash then you have to use a tripod or have the camera on a flat surface to prevent shaky pictures. I also find that the smallness and lightness of the SD series makes my hand shake more than when I'm holding the A series camera with the side grip, so if you find you don't have steady hands this may not be the camera for you.
All Canon digital cameras have a great warranty and are considered one of the industry leaders in the field. So we still give our node toward the Canon series of digital cameras, see which one may suit your need below:
