You would like to have a new lead created in SFDC after every form submission regardless of whether the contact/lead already exists.
When you use the "sync lead", assign the person to lead queue explicitly, that will create a new lead since contacts cannot be assigned to queues. However, this is going to create a lot of duplicates in your database unless your salespeople are converting/merging these leads correctly. Furthermore, these new leads will have no campaign history, no interesting moment, no score.
It's better to use an "Inbound sales rep campaign" in SFDC and attach the person to it using an "add to SFDC campaign" flow step. Campaigns can contain leads and contacts and can have workflows assigned to them.
Who This Solution Applies To
Customers integrated with Salesforce