Originally posted by John Roberts .... I cover the gamut from car wrecks, to group shots, to live action (from the sideline) at nighttime football and basketball games. I need a camera that performs equally well in all of these environments.
I really have only shot with Pentax, and normally stationary objects (landscapes, cityscapes, etc.). All of the cameras will do well for most things. There are some differences. Nikon and Canon tend to do better at sports, as their auto focus systems lock faster. Pentax's auto focus locks more accurately - i.e., a bit slower. In fast moving situations - that can be a difference. Also, when tracking a moving subject from frame to frame - Nikon and Canon also tends to do better. For sports, Pentax lenses tend to be around f4. Shooting nighttime football or indoor basketball in a poorly lit gym, you will probably need at least a f2.8 lens. In this way, you can capture the maximum amount of light at a relatively fast shutter speed (freezing the subject's motion), rather than getting a blur. The Pentax SR - or in body stabilization will help.
Nikon and Canon lenses, especially the ones used for sports - the faster f2.8 lenses are not cheap, and are also fairly large in size. You can get similar lenses for Pentax, like the Tamron 70-200 f2.8, but they run at $750 (just for the lens).
For your budget overall, the Nikon and Canon models (including the lenses) are going to be similar to Pentax - although in my opinion the Pentax kit lenses (WR) with be a bit better, especially for all around applications. You will not be able to touch a weather resistant camera/lens set in Nikon or Canon for your budget.
There are plenty of examples of folks shooting sports here, and doing well, but it does take practice.
So, that is a quick overview....