After nearly three months of using the Canon T4i side by side with the Nikon D5200, I  thought an updated comparison and discussion of the two cameras would be helpful.   I am not going to tell you which camera to buy. They both have strengths and weaknesses and depending on the type of photography/videography you do or plan to do.

Key Points or Differences Nikon D5200 & Canon T4i (650D):

Image Quality

• In most day to day photos (auto mode or manual) you see little difference between the two camera.  There are some shots where extra detail is visible from the D5200 but only after I stopped using the kit lens.  The Canon kit lens seems better and the fact that the T4i with 18-135 currently costs less than the D5200 with a less sharp and less convenient 18-55 lens is worth noting.
• When the pop up flash is used the Nikon wins every time, flash exposure is significantly better with the D5200.
• In lower light the D5200 does an excellent job, The T4i is close but not on par.  You also see a higher dynamic range from the D5200, a better ability to handle a range of light. In lower light the T4i does not do as well and you notice a loss of detail in some areas, a neon sign is a good example.   You see these differences in photos and video.

Performance & Usability

• The T4i feels responsive with very little lag in navigating the menu, switching modes etc.  The t5i is said to be even slightly improved with no mirror flip down while switching modes on the dial.   The D5200, from time to time, exhibits just a bit of lag, mostly I notice it when waiting to review a shot taken with live view on, it takes noticeably longer which leads me to next point
• The Nikon has greater focus point covereage but I find myself using a single point often and have not seen any noticeable differences with focus speed but I have noticed a hesitation from the Nikon when trying to get a burst of shots in, granted these are larger files but the T4i doesn't suffer from this and the other day I was using both side by side on some skateboarders and missing shots with the D5200 because of the hesitation.  Shot for shot in RAW though they do end up very close, both manage about 6 or 7 shots before the buffer fills and they start to slow down.
• The touchscreen makes the T4i a breeze to use and I often find myself using a hybrid approach of buttons and touchscreen, this approach feels very efficient.  I have knocked the Nikon for usability and it does lack the touchscreen but the "i" button does provide quick access to commonly used settings and the programable function button (fn) gives you some customizability that the T4i lacks, though you can program the SET button on the T4.
• The touchscreen is also lovely for reviewing images - pinch to zoom works and "flipping" through images is snappy.
• After shooting the T4i provides quick menu (Q) with a variety of operations, anything you want to do with an image on the D5200 needs a few clicks into the menu system
• Getting picky, there are times when I notice just a bit of distortion around the edges of the Nikon viewfinder, I don't see that with the Canon.
• Arghh - the D5200 does not allow you to change aperture when you are in live view.  The Nikon does let you adjust shutter speed and ISO but does not update live view, for learning and teaching I love the real time feedback you get on Canon as you change shutter speed, ISO or aperture and watch the LCD simulate your exposure.  You can display an exposure indicator.
• The D5200 is not nearly as fun to shoot video with, mostly because of the aperture lock out and lack of exposure simulation in live view. I usually shoot a 1/60 of a second and adjust my aperture and ISO as needed, with the Nikon D5200 this requires a few trips out of live view and back before I am happy.   The upside is the video quality out of the D5200 at the higher ISOs it is quite impressive.

Feature Set

• There really aren't any features on the T4i that are fun, this isn't necessarily a bad thing but when you compare say the HDR mode on the Canon(very barebones) against the HDR mode on the Nikon which actually takes fewer shots but gives you control over processing power - it feels like a pretty simple camera there is wireless flash control which is quite nice and the D5200 lacks but the HDR and the effects menu is fairly simple.
• Nikon D5200 offers effects and scenes and allows you to shoot video in with some of those effects applied in realtime.  The t5i will offer a similar option but this isn't something the T4i allows.
• The Retouch menu in the D5200 is quite robust, not so much on the t4i.  I don't recommend you spend lots of time retouching in camera but the options are there if it is important to you.
• The Magic Lantern folks are working, an Alpha version is available, and this certainly ups the feature set but I am not sure it is fair to talk about in this review, it doesn't come with the camera.

Bottom lineNikon D5200 - Power camera, excellent quality, nice feature sets that suffers from a few quirks, tad slower performance and needs a lens other than the kit to really shine.Canon T4i -  Simple and snappy with tools that help you grow as a photographer, paired with the 18-135 STM is a very friendly and easy to use photo and video machine. Support this site.  Buy the Canon T4i(or T5i) or Nikon D5200 from Amazon