I am planning to buy a Canon EOS 550D with its Kit Lens (18-55 mm) and a prime lens (50 mm 1.8) with my main intention of clicking portrait and landscape pictures. Just yesterday I came across Sony DSLR-A580 and noticed that the features were a bit better for the Sony as compared to the Canon. I referred to this link to understand the ups and downs of both the DSLR's. I have personally used the Sony A580 (with prime lens 50 mm 1.8 and telephoto lens Sigma 18-200 mm) for more than 3 months and I am quite impressed with the quality. I have even used the Canon 550D in stores to get a feel for the quality and in stores I felt Canon was better. I understand that Sony would be a bit more expensive than the Canon with the same setup, but is there really that much of a difference in quality of images and video?
There's no single answer to this question, because it comes down to a lot of personal factors. However, you won't go wrong with either choice. I highly recommend looking at How much do lens lineups vary across DSLR platforms? and considering which system might fit your vision of your working style as a photographer — but not stressing about it too much.
The difference in image quality in an absolute sense is very small. That's because all modern DSLRs offer excellent, amazing image quality, and any debate is between levels of A-grade. These differences are magnified because camera review sites wouldn't get very many hits if they just kept focusing on that positive story — instead, they have a huge incentive to magnify small differences into distinguishing factors.
The Snapsort link you gave provides a good example of this. While Snapsort provides some useful comparison information, one thing it says is that the Sony camera provides "More than 20% better image quality". This is clearly preposterous. The numbers they use — given as the bare "80.0 vs 66.0" — are from some highly-technical sensor measurement scores, which demonstrate some small clinical aspects of image quality, and which barely relate in any way to the actual potential quality of results.
The claim that one model "Distinguishes more than 3x more colors" is also absurd — there's a technically-measured bit depth of "23.8 bits vs 22.1 bits", which both does not correspond usefully to the practical dynamic range of the sensor nor have anything to do with "number of colors distinguished". The higher value is better, but when it's presented as "3× better" that sounds like a big deal — when in reality, it's a difference that humans, even expert humans, can't possibly distinguish without taking careful measurements.
So, yeah. Don't worry too much about these things.
That's assuming there's no deal-breaker lack of functionality for you in one model or another. For example, if you absolutely must have 24p video for a project, this particular Sony model won't do.