I believe that the Canon Rebel T4i has 3 features that will make me decide over it.
First: it has the highest ISO so far for the rebels (12800 expandable up to 25600). What does it means? It means that you will be able to take your pictures in conditions of very low light without getting them blurred. Personally I hate using flash, and this solves my problem.
Second: it can take HDR pictures. What’s that? That is a software function in which the camera will take 3 images of the same picture (one with balanced exposure, one overexposed and one under exposed) and will mix them all in order to get one single image. This solves the issue of back-lit scenes where you can’t see anything in the shadowed area. This feature also opens the possibility for really nice pictures, but you will have to google HDR in order to know more about that.
And third: for those of you who like to shoot video, the T4i has a new sensor which allows you to shoot more frames per second, and also has a several cool software features that allows you to continuous focus tracking moving subjects.
I have a Canon XTi which I’ve been using for some time now out of the auto mode, and I plan to change to the new T4i. If you take pictures in the full auto mode only, I would recommend you to start with a cheaper model like the XTi or a point-and-shoot instead. But if you are willing to experiment with the manual modes, then read the manual (no one ever does) and happy shooting.
You also can see more information about Canon T3i Vs T4i, Check Here