My opinions of advantages of some the more common makes:

Canon: Great upgrade path to bigger sensor sizes later. The best noise reduction in shadow areas.

Nikon: Commited to C size sensors (they can't use a full frame one). Great range of high quality lenses. Colour matrix metering.

Olympus: Leaders in innovation and the only sensor cleaning system that actually works. High quality lenses. Very light to travel with or carry because of their small sensor size. 

Sony: High quality sensor. Good range of past Minolta lenses that are compatible.

Pentax: The widest range of lenses of all - compatible with all Pentax K mount lenses.

Sigma: Outstanding colour reproduction for true colour with no interpolation.

Samsung: Bargain entry level price.

 

 

 

And every one said, 'If we only live,
We too will go to sea in a Sieve,---
To the hills of the Chankly Bore!'
Far and few, far and few, Are the lands where the Jumblies live;
Their heads are green, and their hands are blue, And they went to sea in a Sieve.

Edward Lear
http://www.nonsenselit.org/Lear/ns/jumblies.html