Let's all remember: the original poster is:
Quote:
We'll be doing primarly kids sports, indoor, outdoor, along with the family candids.
Now, for these purposes, neither of the Nikon models is on par with the Canon 20d (the 30d is still an unknown - presumably with the 1/3 ISO increments it will be a better sports camera than the 20d but I can't recommend something that isn't appropriately field tested yet).
The D200 simply has issues with noise at higher ISOs - so as an indoor sports camera it's a poor choice. So, let's compare the 20D to the D50 AS A SPORTS CAMERA (since this is the primary purpose):
Resolution (8mp vs 6 for the D50 - not a big advantage, 2mp isn't a big deal.
ISO Rating (critical for low light sports) - Canon has ISO 3200, D50 only ISO 1600 - that extra stop is crucial for low light shooting. I've shot football games using ISO 3200, aperture 2.8 and had speeds of 1/320. If I only had ISO 1600, that would drop my shutter speed down to an unaceptable 1/160.
Max shutter - Canon 1/8000, Nikon 1/4000 - not a huge advantage - it's rare that you'd hit those marks during sports shooting. But, certainly not an advantage to the Nikon
Drive mode: Canon (5 fps for23 shots) vs 2.5 fps for 12 shots on the D50. This is a HUGE advantage for the 20D.
LCD size: 1.8 for canon 2.0 for Nikon - edge to Nikon but in the realm of sports shooting not a critical factor.
Autofocus: Both cameras about the same - neither one a match for pro level auto-focus but neither one a clear cut winner.
Noise: Both cameras have good noise levels at ISO 1600, but the D50 simply doesn't have ISO 3200 at all.
Image quality between the two cameras is comparable, so given the features specific to sports shooting (focus speed, drive speed, high ISO capability, low noise) the Canon has the better feature set.
So, as a sports lens, the D50 is more comparable to the old Canon 300D it certainly isn't in the league of the 20D. There may very well be other types of photography where the D50 or D200 is the better choice - but not in the realm of sports.
Which brings us back to a recommendation: The 20d is currently the best consumer priced sports body on the market. The 30d should be slightly better (due to the 1/3 ISO increments) but since the camera is just coming out I can't say there won't be glitches with it. The risk is mitigated by the fact the technology is essentially the same as the 20d - there are no big leaps here. If your goal is to shoot sports, the 20d/30d is worth the price increase over the 350D without a doubt.
If the portrait work was more important thanthat would be differently. Since you listed sports first, I assumed it was themostimportant requirement.