SD Card or CF? Which would you chose. If it is SD then forget the 50D since it is CF card only, and one of the main reasons I chose a 50D over a 60D. Of the cameras you mention though the 50D has the best build quality, and a few advanced features that probably won't actually matter that much to you, apart from maybe AF Micro Adjustment, to match the AF to the lens exactly.
Of the rest I would go with the SL1 since it is essentially an "i" line camera in a smaller body. As well as splitting the middle tier APSC bodies between the 7D and x0D after the 60D, they also split the basic line of bodies, in the rest of the world it went to x000 and x00, in the USA it was Tx and Txi. That made the bottom level line of cameras very basic indeed in some features, mostly done by limiting the software controlling the camera. This means that when reading the headline specifications unless you know specifically what you are looking at separating them can be very hard. Sometimes you might only find out that in the lowest range of cameras certain features may only be accessible in very limited circumstances.
For example back in 2005 when looking at the original Rebel, known to us as the 300D, it has AI Servo AF, for tracking moving subjects, but it is only accessible while shooting in "Sport" mode, which meant shooting at ISO 400 only, and in JPEG, not RAW. Otherwise you could only shoot using the AI Focus system, which tries to guess (usually badly) if the subject is moving or stationary. The only way to find this out was to read the manual very carefully, and it was never mentioned in any review of the camera. Of course the fact that it was about £500 cheaper then it's nearest rival meant that it was pretty much the only DSLR you could afford if your budget was £1000 back then.
So I would avoid the non "i" T series cameras if at all possible, they tend to be very limiting rather quickly if you are serious about learning photography. Of the cameras that I would recommend on your list the SL1 is by far the best option, even if it is the smallest in size.
Oh and finally I love my 50D, would an extra 3 MP help? yes a bit, but remember that for it to make a significant difference to the linear resolution, which is what really matters, you need to make a much bigger jump. To double the linear resolution of a 6 MP sensor for example you need to go to a 25 MP sensor, since the sensels have to be spread out in two directions. The more you start with, the more you need to add to make a significant change. Hence Canon going from 18 to 24 MP.