I want to buy a camera. Which one is better?

Nikon D3200
Canon EOS 600D
Which one is more affordable about buying accessories like lenses in the future?
Nikkor is a reliable brand for Nikon lenses?

LOL

You asking if Nikkor lenses are a reliable brand tells me that you need to learn a lot more about not only the fundamentals of photography, but do a lot of research.

NO digital SLR camera system is affordable, not really.

Here is how the sensors of the 600D and D3200 compare

What you will see from this link, the Nikon sensor works the best of the two in low light.

Both Nikon and Canon make the cameras and lenses that the pros use, so yes you will be able to find accessories and lenses for both brands in the future.

You need to do some more research on the Nikon and Canon websites
Read the professional reviews on DP Review and pay attention to what those reviewers have to say.
You have the link to the site that compares the two cameras sensors, so all you need to do next is visit a proper camera shop and hold both cameras in your hands

Being a Canon guy that's all I recommend… Take the 600D

I use Canon and recommend them.
Nikon users will recommend Nikon.
So, toss a coin and decide.

They are all the same. Here's the cheapest one among the lot.

http://www.bhphotovideo.com/...amera.html

If you only know two manufacturers, and think one is better, you aren't ready for a DSLR.

You have to be a special kind of stupid to ask, 'Canon or Nikon?'