CVG is generally more expensive than either DAY or CMH. DAY is the shortest and should be the quickest drive, and is generally less of a problem for traffic than CMH or CVG (particularly if you're in a hurry to catch your flight out!). Southwest serves both DAY and CMH, but not CVG, if they are available to you from where ever you are traveling. Sounds like staying the night isn't really an option for you. What boiler said is spot on. Good luck!