Which DSLR camera brand do you prefer? And why?

I'm trying to search for a good camera to buy. Canon or Nikon? I was focused on getting a Canon but now I'm reconsidering because Nikon might be more cheaper and whatnot.

My budget is $600 and lower, I'm not interested in buying a real expensive camera right now but I do want to buy an SLR camera.

It would be nice if you could also tell me what to look for when buying a SLR camera, thanks!
I know some of the aspects already but more advice is great.

They're both more or less on par with each other. They like to leap-frog every year or so over who has more features on their cameras, but like I said, more or less equal.

You're much better off going to an electronics store and trying out the cameras in your hand, then choosing the one that feels the most comfortable to you. Honestly, at the <$600 range, ergonomics is probably THE biggest difference you'll notice. I'd recommend the Canon Rebel XS, Nikon D3100, or Canon Rebel T1i in your price range. Go try them out in store, then go on adorama.com or bhphotovideo.com afterwards and buy them (usually cheaper prices than Best Buy and such).

As for me, I prefer Canon for many reasons. I find their bodies to be more comfortable (but again, this is a personal thing, and might not ring true for you). Also, all their lenses work on all their DSLRs, whereas Nikon's cheaper/older lenses won't autofocus on their entry level DSLRs (they lack an in-body motor so they can only use AF-S lenses, not AF). As a result, when I started out with photography Canon had many cheaper primes to choose from, and my personal style revolves around a set of primes rather than a zoom lens. Finally, for me their lenses are pretty affordable. A 28mm f/1.8 USM, 50mm f/1.4 USM, and 85mm f/1.8 USM are cheaper than their Nikon equivalents while featuring an ultrasonic motor, which I absolutely love for its quick and quiet autofocusing.

With that said, I'll reiterate again: I'm a dedicated Canon user who will recommend both Nikon and Canon equally.

EDIT: @LovingYou: There actually is a huge difference between the D3000 and other DSLRs. The D3000 uses a CCD sensor whereas other DSLRs use a CMOS sensor. This means that while the D3000 is fine at normal ISOs, it has worse noise than other DSLRs (including the similarly priced Rebel XS) at high ISO. This is why I purposely left the D3000 out of my recommendations.

600 brings the Nikon d3100 in your price range as well, fine camera that is.

At the end of the day what matters is that you get something that feels right to use for you. And that's personal. Canons and Nikons in the budget class have a distinctly different feel and controls. For me Nikon works and canon does not, for other people it's the other way around.

I get Pentax dSLRs to be able to use my old screwmount prime lenses with the benefit of a working in-camera lightmeter. The fact that Shake Reduction and Focus Confirmation works even with my decades-old lenses is a welcome treat.