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The field with a (letter) after them are custom fields that would have been created in Salesforce and synced to Marketo. This means that the field labeled Company Name is the original, and most likely the one you want to use. If you look at the CRM Mappings for each field in Field Management, that will give you clues as to what object they were created on, and you can hide those you're not using.
In addition to John's point,
Click on these fields and look to which CRM fields they are mapped with, it will give you a hint on their origin. You may find out they come from additional, unused, fields in you CRM that have been mapped to Marketo.
Thanks Greg & John. I will investigate.