If there was a right answer as to questions like these there would only be one company making cameras.
Unless there are certain features or accessories you need that one has and the other does not, it really just comes down to personal preference.
If you cannot decide between the bodies look at the respective lens ranges and see if one has better options for your needs, or works out cheaper.
As for the 40D, it looks very nice to me with a number of very attractive features over the 30D. Although being a new model it will be starting at around £900 in the UK as the list price for the EU is 1299.
With it being only $1299 in the US hopefully Kerso might be able to do it for a decent price though.
Michael.