Likert scale radio buttons: default choice?

We are making a simple Likert scale radio group for feedback and will group it as follows:

Please rate the service you received:

• Very poor
• Poor
• Average
• Good
• Very good

According to usability guru Jakob Neilsen, radio choices should have one option selected as a default. In a typical Likert scale like above, what would be the most appropriate to select as default? 'Average', as it is in the middle or 'Very good', which might appear presumptuous?