I have a both. Unless the price difference is a deal breaker for you, get the 20D. You can buy a used one for about $950. I'm not sure what a used 10D goes for now, but I'm guessing it's around $750. If you are going to buy a new one, then get the 20D for sure. If you decide you are going to buy the 10D, then let me know. I will be selling mine soon.
John, I'm assuming you're using this is as a backup, considering your impressive body collection. I just went from a 300D (unlocked, almost 10D functionality, same sensor etc) to a 20D. While I haven't had a chance to really stretch my legs with the 20D yet, I can say without a doubt find a 20D. The startup time alone is worth the extra money. It takes a 10D two full seconds to power up, even when in standby (auto-off) mode. The 20D powers up so fast you wont even notice you had it off. You just press the shutter release and it responds. IMO, it'd be less of an adjustment to your shooting style if you're using it as a second body while using one of the 1 series or even the 5D.
Thank you for all your comments. In case you were wondering this body is for my 10 year old son. He wants to photo what I do so I think the 10 d was a good choice.. I was thinking of geting the 10d with Tokina 12-24 F4.
Anyone noticed the difference between color of a 10d vs 20d? Some people i've read that the 10d has better colors?
John, I recently did what you're contemplating doing - bought a 10D for my teenage son to learn digital photography. You should expect to pay between $600-700 for one in good condition. He's going to get it for Christmas so I only used it for a few test shots. Compared with my 20D I think it's a good value for the money. Despite the older technology, the colors and sharpness (jpeg) look great straight from the camera. I also bought several lenses for him: Sigma 15-30 for wide angle, Canon 28-135 for mid range zoom, 50 1.8 for low light, and 70-200 f4 for the long end - so he'll start with everything he should need for a long time.
The 10D is a great camera and they run about $750-$800 for a camera in good to excellent condition with a grip and two new batteries (make sure the seller is getting at least 400 shots per battery, other wise replace it -- a new battery is close to 1,000 shots per charge). The 10D is slower in every conceivable way than the 20D, but is a nicer feeling/handling camera and has a better, brighter viewfinder. You have to think about your photography a bit more with the 10D. Focus on the 10D is slow, but in my experience very accurate.
As far as specific things to be aware of besides the battery, nothing comes to mind. New batteries run about $20/pair from Sterlingtek when they are running a sale and they seem to be high quality.
