Depends on if you want that field to ultimately exist in Salesforce. If so, create it in Salesforce and let it sync over. If you don't want it in Salesforce, you can create it in Marketo. Personally, I don't think it's important to have Behavior Score in Salesforce as long as you have Lead Score in Salesforce.
Thank you. I feel like I am on the right path yet really far away as it isn't reading to Salesforce and overall I am not getting anything but by campaign I am. I will attack again tomorrow with a fresh brain. Hoping to have that air fist pump moment.
If you are trying to import your lead scoring programs that you've built from one instance to another (Sandbox to production) then you need to make sure the fields exist in the instance you are trying to import the program to.