- why would you guys stay with Canon?
We love Canon. Even if Nikon gets better sometimes.
- The image quaily between Canon and Nikon are different?
Depends on camera model. Right now Nikon D800 (sensor made by SONY) has arguably the best IQ in the world. Not for long. So, you should be asking if image quality between Canon and SONY are different.
- Is canon's noise performance really bad compare to nikon?
Check the tests.
- Pros and cons for each brand
They're both great, innovative, established photo brands set apart competition. If we need to say, Canon has fantastic lenses and diverse range, the L series is legendary. But it all depends on your budget. Nikon is a school of its own. Has seen a lot of rugged action since the film days. That's enough to make a name. In digital imaging Nikon never caught up. They left it to SONY.
- P.s I am taking for both landscape and portrait
Landscape, check the works of Art Wolfe and his gear. Portrait, the EF85/1.2L II is the best lens in world as we speak. From the 600D you'd probably upgrade to Canon 7D. Fantastic model and vastly improved with the latest firmware. Look no further.