We have already integrated Marketo with Salesforce. but still we have about 200K+ marketo leads that are not synced to salesforce yet.
What is the best way to sync these leads?
is creating smart list with sfdc type (is empty) and use "Salesforce -> Sync Person to SFDC" is best way to sync?
You should be move this question to Product discussion where you can get more visibility.
You can create a smartlist with SFDC Create date is empty or SFDC ID is Empty and then Sync to SFDC. Please make sure all the required field are valid and also if the email address is correct before you push them through.