If at all possible visit a bricks and mortar store where you can handle cameras from several manufacturers. As a Pentaxian I am totally unbiased

but I think you'll find that the feel of a camera in your hands is as important as the breadth and depth of lenses and gadgets and whatever available for it. Canon and Nikon make fine cameras, as does Sony, but the Pentax feels better to me. Of course, YMMV. Try to compare them with equivalent lenses, for example the ubiquitous 18-55 kit lens, and compare the brightness and size of the viewfinder image. Can you use it with glasses? BTW, few if any DSLRs have viewfinders as bright and large as the better film SLRs. Such is life, I suppose.
Pentaprism finders are generally better than pentamirror finders, although they are more expensive to make.
Unless you demand the newest, a good time to buy is just after a new model is released. While there are sometimes dramatic improvements in a new model - the Pentax K 3's increase in sensor pixels and its switchable anti-aliasing filter, for example, generally changes are incremental.
Used gear is another possibility. Since most DSLRs have a shutter count feature you can tell the "mileage" so to speak. Adorama, B&H and KEH are all reliable dealers, in my experience. Just make sure you get ALL the goodies vital to the camera, like a battery and charger, for example, and any software included in the package.