Nikon D300s vs Canon 7D with high ISO?

Which one is best?

These two cameras are really very close. It's more a matter of whether you prefer Canon or Nikon. Here is a comparison of the two.
http://snapsort.com/...ikon_D300S

You really need to take yourself down to a camera shop and see which one fits your hands the best.

Here is a sample of the older D300 at ISO 3200 posted at a reduced resolution of 600 x 400 @ 72 dpi.

As you can see at that ISO setting, there's little noise.

Of the D300s and 7D the dynamic range of the D300s is slightly better than the 7D and the high ISO performance is slightly better with the 7D.

In practice, you need to do some tests, but I don't know how you are going to do that with any accuracy without renting each and doing your tests.

If you look beyond those two camera bodies to the Nikon D3s and Canon 1D, Mark IV, you will see that the Nikon system has had the edge in the high ISO ranges since the introduction of the Nikon D3 in August 2007, the D3s improved its standing. The "system" performance using high ISO's are much more important than any individual camera body.

If your goal is to have a system that performs well at high ISO's, then you need to do more research, not get opinions

While agreeing with both answers above, I've shot both cameras extensively. The difference is negligible if you are shooting RAW. The in camera default noise reduction settings when shooting JPEGs will make the Canon appear to be slightly better but, those can be adjusted to suit user preference. More important differences lie in the controls and overall camera layout and while I currently shoot the 7D (along with the 5D Mark II), I think the D300s' control layout and the setting information available in the viewfinder are better than my 7D. I chose to stick with Canon largely because I was already heavily invested in trhe Canon "system" of lenses. At the time I started shooting with Canon, Nikon lagged behind Canon in high ISO image quality. As Fhotoace said, this all changed in 2007 with the release of the D3 and D300. But I will say that making a decision based on who has the better system at this moment comes with risks of deciding you should have gone a different way later.

Canon and Nikon have leapfrogged each other in terms of technology for as long as I have been alive (literally). When I was a child, Nikon ruled 35mm film cameras because they had the best and widest range of lenses as well as robust cameras. But when I was a teen, Canon's EOS system became the cameras and lenses of choice for many pros shooting sports and other events because their autofocus systems were faster and became essential for keeping up with action. Nikon during this time was used mostly by folks who had lots of time on their hands to shoot models, mountains and other stuff that stood still long enough to shoot it on a tripod. As digital cameras became the new standard, Canon initially continued to lead in sports, mainly because of their faster autofocus and later because their CMOS imagers were better for high ISO shots. In many other areas however, Nikon has continually offered innovations that are just now being seen on Canon cameras like the 7D. The 7D's built-in, wireless flash control is a prime example. So the point lurking here is "retiredPhil" is right, you really need to go try these cameras out in person and decide for yourself which works best for you. I'm looking at the possibility of switching back to Nikon but, I'm waiting to see what Canon is going to do with their replacement for the 5D Mark II and what Nikon does with their replacment of the D700. I've grown to prefer Nikon's control layout on the D300s/D700 bodies but, I'm not moving if they dumb down or otherwise screw up the replacements for these bodies.