18-200mm is a DX lens whereas the 70-300 is a FX lens.
As you are using the D40x, the 70-300 becomes a 105- 450mm on a DX body due to the crop factor, whereas there is no extra gain on the 18-200mm lens.
I own both lens and initially started out with the 18-200 as my "holiday" lens on my D300 to minimise carrying around too many lens etc.
Bought the 70-300 together with my D700 2 months ago but ended up sticking it onto my D300 to gain extra zoom advantage and not having to move too close to the subjects as you have also noted in your post. Photos tend to be a bit soft once you zoom past the 240mm mark.
Must admit that I am a newbie, started DSLR with my D300 only last October, but I found that even with VR, at 300mm (450mm on DX) and slight handshake is very evident and tripod or some form of mounting/bracing is required if you are not shooting in optimal lighting conditions.
70-300 is a light lens and great if you need the Telephoto zoom on a DX body, otherwise the 18-200 covers a good wideangle to zoom range and is a better/more solid build with faster response.
Choosing a lens always boils down to 2 basic questions;
- How much am I willing to spend?
- What application is the lens intended for?
once answered, then work your way from there.
