Have you cleaned your sensor, does it respond to a Rocket Blower? What was the result? A higher resolution camera will show fine grained dust more than a low res sensor so some dust is expected as is cleaning occasionally. It is an easy do, quick, general maintenance that camera owners learn to do. One thing to consider, even with some dust, the sensor is probably the cleanest surface you have in your entire environment. Macro or photo-microscopy will show levels of everyday dust and particulate matter that we never are aware of.
Your sister has a beautiful collection of photos. If you exchanged cameras with her for a week, her images would probably improve on a technical level since you have more dynamic range, higher resolution, lower noise, wider color depth etc than she has regardless of which model. Once cameras because better than just good enough, it has little impact on subjective image quality. Only when comparing side by side in minute detail.
I doubt many people have moved from Nikon to Canon but recent models of Nikon's have attracted a lot of Canon users, particularly the D800, D4 and D600. Before that the D3s has no equivalent. Any of these cameras have lower artifacts and banding than any of the Canon models. Even with these advantages, Nikon photos are no better or worse than those from Canon cameras, because non-photographers grade images and art by their own emotional reaction to them and not on technical aspects. A well composed, well communicated concept will be appreciated by most regardless of its technical quality. There are many highly skilled illustrators who can accurately portray the physical world but their technical quality will seldom elevate their work to be appreciated as widely as fine art images, usually paintings, by masters who are or are not as technically skilled, but more expressive or communicate more effectively. Exactly the same situation exists with photography.