contact match script?
Step 1 - Use a program to make your data consistent.  There are lots of possibilities out there - try OpenRefine (open refine.org).

Step 2 - once consistent, try to assign the contact.id (aka contact id, internal contact id) to a column.  This will remove de-duplication issues

Step 3 - Import

Its really hard to have a script that finds inconsistencies, and they vary so much across data sets: some have all sorts of titles, others have improper address (street vs st vs str), etc.  I find its almost always less time to invest in work before the import instead of counting/hoping on finding duplicates later.