The t3i is technically two versions older than the t5i. However, the differences between the t4i and t5i were very small and virtually irrelevant, so for all intents and purposes the t3i is really only one version older, not two. If you are planning on shooting video a lot, the t5i is a better choice along with an STM lens, even though the t3i takes great video as well. If, however, you plan use the camera for stills only, save the money and buy the t3i. It uses the same sensor. While, as noted, the frame per second rate of the t5i for sports action is a bit higher, and perhaps it also has slightly better low light performance, and of course a touch screen, other than that the two cameras are extremely similar. If photography becomes a passion for you, you will likely outgrow either one in due time. In the meantime I would go with the cheaper t3i.

The number of pixels is important for print size, but if you edit your pictures, it is really important in relation to crop size. For example, if you take a group picture of 20 at a family reunion you willl likely have no problem printing an 8 x 10 of the group with just a two megapixel camera.

But, if Aunt Meg later asks if you can isolate Uncle Ralph and print a large portrait of just him, the answer will likely be no if the picture is 2 megapixels, yes if the picture is 24 megapixels. This also effects cropping out just a bumble bee on a sunflower photo to display on your big screen TV and so on.

I have a 2, 8 and 24 megapixel camera's. For me, the 8 meg is a nice size, the 24 is a bit large, but, I like a bit large. If you are like me, and keep tons of not so great pictures of pets, kids, family, it's not very efficient keeping 24 meg files of pictures you will never edit or print. I don't mind much with the 8 megs, but the 24's I have added an extra step and reduce the size in a batch process of all the ones I deem not worth keeping in large format. It takes a second to do, much longer to decide which ones I'll never want in large format.

Also, the larger the format, the more processing power it takes to work on the photo's. So, other than a little space, and some computing power, there is no downside to more megapixels.