There is really no way to objectively analyze the saturation of photos from any brand of camera. There are far too many factors involved, far to many layers of indirection, that create a lot of "noise" that obscures an objective result. A lot of review sites certainly try to produce as objective of comparisons as they can, such as DPReview and DXOLabs, however you have to take it all with a grain of salt.
Here are the facts:
- What you see on your screen is not necessarily what others see on theirs.
- Computer screens all produce different results, even when properly calibrated.
- An uncalibrated screen may over saturate or under saturate, preventing you from seeing the "actual" photo
- What you see in print is usually a greatly reduced level of saturation and dynamic range
- Prints, which often look excellent when viewed in a proper setting under proper light, are often mere shadows of what the camera actually captured
- Dynamic range and bit depth of modern cameras tends to surpass all but the most expensive screens and printers
- Most cameras these days have 12-14 stops of dynamic range
- The best computer screens may have as much as 10 stops, but usually only 6-8 with cheaper screens
- The printers with high dMax may be able to achieve 7 stops of dynamic range, but realistically you may bet 5-7 stops
- Lower dynamic range reduces contrast, which affects saturation
- Post-processing enhancements account for a significant majority of the "wow" and "pop" factors that give a photo its emotional impact
- Saturation can be enhanced significantly during post processing, either directly, or via exposure tuning and contrast enhancement
- A lot of the artistic style of a photographer is achieved with post processing
- Two photos of the same exact scene at the same exact location taken with both a Canon and a Nikon can be made to look identical to each other with post processing.
- Any technological differences can be entirely eliminated or hidden, as in the end, they really don't mean all that much...the photographers vision and style means far more
- Most IQ tests are done at 100% crops levels (full size, pixel peeping) and do not reflect real-world viewing situations
- A significant amount of photography is viewed online these days, at tiny resolutions that on-screen approximate 4x6" to 5x7" print size
- Most prints involve significantly higher pixel density than a computer screen, and higher pixel density absorbs undesirable artifacts, noise, etc.
- The IQ measurements of a 100% crop are useful from a statistical comparison standpoint (think using DXOLabs to compare the low-level hardware capabilities of two cameras)
- The same IQ measurements of 100% crops are largely worthless from a real-world standpoint...good gear can help you fully utilize your capabilities, but its really the capabilities of the photographer that matter.
My best advice to you is to buy the camera that feels best in your hands, and gives you the functional capabilities that allow you to best utilize your skill. The minute technological differences between a D5100 or a 550D are inconsequential, as they are largely equivalent. If the 550D captures more "realistic" color and the D5100 takes more "saturated" color, but the 550D feels better in your hands, get the 550D. You can easily enhance saturation with RAW images in post processing, along with pretty much anything else that may not fit your style.
The only meaningful differences in camera equipment generally involve the things that cost more money. A low-end camera will usually offer minimal features, and while you can certainly take excellent photos with such a camera, you may find some things more difficult to do, or requiring more effort, than with a more capable camera. It doesn't matter if you choose Nikon or Canon, a more expensive model from either will usually include better AF capabilities, making it easier for you to capture subjects in motion and action shots. A top of the line camera will usually bring a much higher frame rate to the table, allowing you to fire off 10-14 frames per second rather than a mere 3-4. The actual photos you capture that are keepers are likely to be unchanged, and you will still have to apply that artistic prowess in post to add your personal touch, your style, to the photographs you take...but better technology can increase the number of keepers.
Minor things like which brand produces more "saturated" photos are moot points in the face of an advanced AF system that lets you nail focus every time on that figure skater, or that airplane, or that elk during a rut...so don't worry about them.