Probably each site about photography has its own tips how to choose a camera. This one is not an exception. In general, all are speaking about Nikon vs. Canon vs. Pentax etc. This actually does not matter. All of them are really good. The main tip I found most useful (couple of my friends as well - they made a choice based on this) is to hold the camera and see how it fits to your hands. Then you will decide, as this criteria is really important (imagine some irritating feature of camera which will annoy you each time you hold it). The only thing to consider choosing between manufacturers is lens options and the level of camera. As always buying the cheapest one brings no good, though buying too expensive is waste of money - you must keep in mind that really important thing is lenses which cost a lot (thus instead of buying top notch model you can opt out for better lenses). As you might guess Canon and Nikon has the biggest number of lenses to choose from. I would say, that you should not rule out such manufacturers as Sony or Pentax - they have their own lenses, also third party ones for offer (like Sigma etc).
Personally, I opted for Nikon mainly of two criteria - holding a camera and a very good discount provided for camera and two kit lenses. I did not consider other than Nikon or Canon as probably everybody would agree that those companies are the leaders (not only in cameras but also in lenses with biggest selection).
To sum up:
- see what is you budget;
- see what cameras are available with your budget (including lenses);
- hold them and decide which you like mostly and which fits in your hands; that is your choice.
I advise like this because generally all manufacturers provide approximately the same quality with slighty different options, so if you want to shoot instead of counting pixels, just grab the camera which was created for your hands and use it. Don't waste your time in trying to find out which camera has slightly lower noice at stupidly high ISO.