It's a nice dilemma to have, dandan.
Personally I'd go for the 40D because the controls and feel of the camera suit me, but they are both very good. In particular I like the wheel thingy on the back of the 10/20/30/40D which the 450D doesn't have, and also the size fits my hands better, especially with larger lenses.
Although the 350/400/450D are excellent, I haven't come across anyone who has upgraded to the 30/40D and regretted it.
I'm waiting for the 50D. Honest!
