I'd go new, definitely four stroke, probably Yamaha. My justification is: 1) It is probably the most used item on the boat. Why not buy the best for something you use so much? 2) Generally a new four stroke Yamaha will give you ZERO problems and make fishing even more enjoyable because it is whisper quiet. 3) Resale on kickers is incredible...buy a new kicker, use it for 10 years and you can probably sell it and still get half of the new price for it. In this scenario, I'm going to pay for the first 10 years and let someone else pay for the next 10 years!

Convinced?