First DSLR - Suggestions

You won't go wrong with either system.  There are some differences but both brands sell extremely well for a reason.

The 18-135 STM lens seems interesting.  However it is only an average quality lens.  Nothing worth spending alot extra for unless video is a big concern (which is what it is designed to be helpful for).  A slightly better lens would be the Canon 15-85is.  Sharper, faster focusing, not known to have decentering issues, etc.  The 18-55is is better optically based on reviews than the 18-135, but not enough to worry about.

For general photography, the Nikon 18-105 is sharper, lighter, and cheaper than the 18-135.  The Nikon 16-85vr is the next one up in quality but the 18-105 is so good that most do not pay extra for the fairly minor gains the 16-85 offers (I shoot both at the same time and kept the 16-85).

The t3i & t4i are basically the same camera.  Very little difference.  The main one being that the t4i is slightly faster in video AF.  But it is still terrible, just "less terrible".  The sensor in this camera is well-behind the times now.  Canon should have replaced it with one more competitive with the d5100 or current Pentax and Sony offerings.

The Canon 60d is a better body.  It has better controls, better ergonomics, better viewfinder, better build quality (incl. weather sealing, if you use a weather sealed lens).  But it has the same sensor and so image quality will be identical.  But if I have a bunch of high-end Canon glass, particularly EF-S (APS-C) lenses then I would be looking at the 60d or 7d.  To ME the quality difference in the camera is worth the difference even if the sensor is identical.

The d5100 and d7000 also share a sensor.  But it is a better sensor.  It has better low light performance, better dynamic range, better color sensitivity.  And low light here does not mean shooting in pitch black but typical indoor lighting with moving subjects.  Both are available with the very good 18-105vr kit lens.  Locally (Norway) the d7000 is also avaialble as a kit with the better (but more expensive) 16-85 and as a "bundle" with the weather sealed 17-55 f2.8 (there is no canon equivalent as Canon's 17-55 is not weather sealed).

The new wrinkle in the Nikon world, the d5200.  With an all new sensor.  It also inheirets the more advanced focus and metering of the d7000 instead of the one used in the d5100.  Like the d5100 it has an articulated rear LCD (which I do not care about, but some like for Macro).  For now the d5200 is avaialble in Europe and Asia but within 2 months it should also be available in the USA.  In the meantime this is pushing down the price on the excellent d5100 and d7000.

I like the d7000 more because it has a better build quality, weather sealing, a higher end viewfinder (pentaprism instead of pentamirror), better autofocus and metering, better support for very old lenses, better ergonomics, better controls.  Unless one of the Canon bodies has some specific feature of function you need, I'd recommend the Nikon d7000 over any of them because of the better sensor and essentially identical lens selection.

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See my plan (in my profile) for what I shoot with. See my gallery for images I find amusing.