Brands
85% of all DSLRs sold are sold by two main brands; Canon and Nikon. There are also fine offerings from other manufactures such as Pentax, Olympus and Sony. All are excellent manufacturers that have been around for years dating back to film cameras (Sony's was previously under the Minolta/Konica Brands). No one manufacturer is better than another and they all have their strength and weaknesses.
You just need to find one that has the strengths in the areas most important to you.
There are often huge flame wars between Nikonians (Nikon shooters) and Canonadians? (Canon shooters) about which brand is superior, which I always refuse to get into. I happen to shoot with Canon but my images would look no different if I shot with a Nikon. I have never heard someone standing at a gallery show, saying "Wow - That is such a great Nikon shot", or "There is some real Canon magic in that image". When it gets to that point (large print on a wall) no one would know. It is all about features, controls, and specifications that fit your needs, not brand popularity.
So let's look at some of the technology and features of a DSLR and I will talk a little about what brands may have an edge in certain areas. But the superiority of one brand over another is very close, and who is ahead may just depends on the new model release of that year.