I bought this camera for Christmas 2012. So far I am quite impressed. This is my first Digital SLR (I shot 35mm SLR, and Digital Mirror-less prior). I purchased this over the Nikon D5100.
The Nikon does produce less noise at higher ISO's, than the T3i does, but I don't generally shoot fast and/or night action, so It hasn't been a problem for me yet.
Auto-focus is quite quick and intuitive. I actually prefer Nikons focus-point layout better, but the T3i seems to be a bit faster auto-focusing, and the view-finder is far superior I think. Unfortunately there is no continous auto-focus for video on the T3i. The D5100 does auto-focus in video mode, but it is quite sluggish at best. I have a dedicated video camera, and when shooting video with the T3i, I prefer a manual follow-focus anyways. So no major points lost there as far as I'm concerned.
Both cameras have great LCD's. However the T3i does not crop the image unless you are shooting specific formats. Otherwise it maintains 3:2 aspect-ratio full-screen. The Nikon D5100 crops the image in the LCD and uses the border for camera info, whereas the T3i has the information overlayed on the image (and can be toggled on/off with live-view Hstograms, which makes setting exposure quick and easy).
Video quality is quite good. Shoots 1080P at 30/25/24fps, and 720p at 60fps (no 720p at 30fps though). Again, no auto-focus, but for those serious about shooting film with the T3i, there is an excellent freeware operating system available online called Magic Lantern (I neither endorse nor condone). It offers a host of upgraded video features such as HDR Video, Custom frame-rates (720p at 30fps after-all), video effects, and zoom options, plus extended ISO range, Shutter speeds, intervalometer, and bracketing features for HDR, among a thousand other features.
I got my T3i with the 18-55mm Kit lens, and 55-250mm zoom lens. Both do a good job considering their relatively inexpensive price. Serious photgraphers/videographers will want to upgrade the lenses for sure. Canon makes a great little 50mm F/1.8 for right around $100, which is great for video. But these 2 lenses are really good all-around "Bread and Butter" kind of lenses, that will allow everyone the ability to learn and hone their skills. My only real gripe is the 18-55mm doesn't have a dedicated rubber focus ring on the lense body like the 55-250mm does. But rather, is located at the very front of the lense, is thin and plastic, and somewhat recessed in comparison to the main body, which makes it somewhat elusive when reaching for it in a hurry.
The T3i features both IR remote, and Wireless flash control as well.
Overall I am happy going with the T3i. It really is just "Apples and Oranges" when trying to compare it to the Nikon D5100. In the end what really sold me was:
- The grip felt better in my hand (I have big hands)
- The menus and infromation onscreen, are far more intuitive
- The controls seemed better layed out to me
- Histograms available in live-view (Nikon D5100 only has in image review)
- A relatively cheap upgrade to a fast 50mm lense (of course there's always the Canon L series ;)
I would recommend this camera to everyone!!!