To request for deferred sentencing on a speeding ticket, which box do I check off? Mitigation Hearing or Contested Hearing?

If you are eligible you will want a contested hearing and the Judge should offer the deferment program. If not you will have to ask when you are called.
Good Luck

In most courts either generally works, but check contested to be on the safe side...the real issue though is that you should consult an attorney in Kirkland (feel free to use one of the links below) to analyze the ticket and possibly contest it for you. It may be that you can save your deferred finding (only one per 7 years) and get a dismissal instead! If you got one, there is at least a chance that you will get another sometime in the next 7 years...

This answer is not legal advice and is for general informational and/or educational purposes only. No attorney-client relationship is formed between you and Sean B. Malcolm, an attorney licensed in Washington. For more information, see the Avvo.com terms and conditions of use, which are incorporated by reference herein, and www.valdezmalcolm.com.

Mark the Contested Box, keep a copy of the ticket for your records, send the original to the court within 15 days of receipt. I also advise that you contact an attorney as you may have other options besides deferrment.