There is no "best" area of Louisville - each area has it unique qualities that may or may not appeal to you as an individual. The police department would be the place to inquire about crime rates in any area.
There are certainly areas of Louisville that have a lot more crime than others. If you want lower crime and more expensive homes, then look to the east side of Louisville, or even Oldham County. Check out the crime maps here on Trulia or lookup crimereports.com.