Kiln dried logs are artificially dried in large ‘ovens’, an expensive process which is reflected in the price. If wood is properly seasoned, there is no real benefit to kiln dried over naturally dried wood.
Soft wood is less expensive than hard, but if not seasoned properly it will hiss and spit. If it IS seasoned, it will generally burn very quickly and not produce much heat therefore requiring you to constantly add more logs and get through your pile more quickly!
Burning soft wood contributes a great deal towards tarry deposits in the chimney flue, meaning you will need to have it cleaned more regularly and if not may lead to chimney fires.
The term “moisture content” is often mentioned and ideally this should be below 20%.