Which one of these is better, canon and nikon?

Why do canon dslr restrict itself to 18mp where as nikon has 24mp? Does it make any major difference in the quality of photography?

Not really, but cramming more megapixels onto a sensor without increasing its size is a good way to sell cameras to people so thick, that they can't see beyond Canon and Nikon.

There are many questions you should ask before buying an expensive camera, 'Canon or Nikon,' is not one of them.

They are basically the same. Megapixel count doesn't matter much. Picture quality is highly dependent on the skill of the user.

The first thing you need to learn is this: "It isn't the camera its the photographer." Sony, Pentax, Nikon, Canon it doesn't matter. What matters is your knowledge of Light, Composition, Exposure and Depth of Field (DOF) and your skill in using that knowledge. The knowledge comes from studying those four components of photography and then practicing using that knowledge to develop the skill required to use them to make the pictures you want to make. This site has tutorials on them suitable for the beginner: http://digital-photography-school.com

In my opinion Canon has sort of stagnated in introducing new cameras. All they've been doing is using the same sensor in "new" models that as often as not offer minimal upgrades compared to previous models. Canon introduced the 700D/T5i which is a minimal upgrade to the 650D/T4i and quickly dropped the 650D/T4i. The closest they have come recently to being innovative is the 100D/SL1 which they're calling the smallest and lightest DSLR available.

Nikon, on the other hand, has been more innovative with their newer models.

While both Nikon and Canon offer an entry-level lens line (designated DX by Nikon and EF-S by Canon, there's a major difference in how those entry-level lenses can be used on different DSLR camera models.

The Canon EF-S lens is designed solely for their crop-sensor cameras such as the 700D/T5i and 100D/SL1 and an EF-S Can't be used on a Canon full-frame DSLR such as the 6D, 5D or 1D.

Although designed for their crop-sensor (DX format) DSLR cameras such as the D3200 or D5200 or D7100, a Nikon DX lens CAN be used on a Nikon full-frame (FX format) camera such as the D600 or D800 or D1 or D4. This is possible because Nikon allows the used of one of their FX format bodies to "tell" the camera a DX format lens is being used and the camera "crops" the FX sensor to the size of a DX sensor.

So someone who buys a Canon crop-sensor DSLR and adds 2 or 3 EF-S lenses and later decides to upgrade to a Canon full-frame DSLR will have to replace all of their EF-S lenses and that is an expensive proposition.

Someone who starts with a Nikon crop-sensor DSLR and adds 2 or 3 DX format lenses and later decides to upgrade to a Nikon FX (full-frame) DSLR can at least use their DX format lenses while saving for FX lenses.

Another plus for Nikon is that they have used the same lens mount since 1959. A Nikon lens made in 1959 can still be used on any current Nikon DSLR although some limitations will apply - but at least those vintage lenses can still be used.

Canon, on the other hand, changed their lens mount in 1988 so there's limited backwards compatibility with them.

I prefer canon rather than Nikon. There's no as such difference in the quality of photography…