If there isn’t too much of a price difference and if you can find one in decent condition, I’d go for the 20D – you’ll be getting a much more professional camera. Yep, the image quality between the two are pretty much the same… but the difference is that you’re likely to get better shots more often with the 20D (imho). It’s sorta like comparing two rifles… they might shoot as well as each other – given that conditions are constant – but when conditions are contantly changing, you’ll likely notice the difference between “professional” and “prosumer.” I hope that makes sense.
Dont’ get me wrong tho, the 350D can definitely hold its own… but when compared to the 20D, the “small” differences can amount to be a lot – depending on what your needs are. It might be worth the extra time shopping around for a decent 2nd hand 20D if speed, handling, and [better] focusing are important for you. I’m pretty happy with my 350D and I have no regrets about going with it. When it came down to making a decision between the two (at brand new prices)… the differences at the time weren’t enough to go for the 20D. Honestly tho, I wasn’t really thinking far enough down the line cuz I shoot a lot more now than I thought I would then heh. So yeah, sometimes I do wish that I went with the 20D – for the handling, better focusing performance, and the two extra focus points… two doesn’t sound like a whole lot but I’m sure it will come in handy when there isnt much to focus on (like at night or when really dark). Again tho hehe, I’m pretty happy with the 350D… just have to work a bit harder with it is all. Anyhow, hope that helps.