whats the best fuel for new car break in?

Whatever fuel you get make sure it has low nitro with high oil content.

yeah just use the fuel that your are going to run your engine on, some people like to run a low nitro high oil content for break in but I have never had a problem running my race fuel for break in just make sure your engine has a nice rich setting with good oil spitting out the exhaust and you wont have a problem when breaking in.
cheers