Database conversion is always a tricky proposition.  Everybody wants all of their data imported even if it's not really accurate.   My basic advice is to do the following:

If You Use Quickbooks

Import QB Customers

Import QB Vendors

This will set up Contact Records for all Customers and Vendors

Then If using Outlook

Import Outlook Contacts

This will Update any previously created contact records with addresses and Email addresses if found along with telephone numbers.

Any Contacts not found will be added as Contact with no type 

When you open a Contact with no type it will ask for a Contact type then create the supporting Properties file.