Having eaten at both, many times, I prefer the Yachtsman.
We generally have better service at the Yachtsman, it's not as crowded or cramped feeling, and for the prices, I want a more quiet dinner experience.
Le Cellier still has the theme park feel; not sure if it's due to the tables being so close or the fact that many people have all their theme park gear with them (clothing, cameras, shopping bags, etc).
The food has been excellent at both. The porterhouse I had at Yachtsman remains to be one of my favorite steaks I've had on property. Polo shirts and shorts would be just fine there.
True, the theme of Yachtsman is a little weird\confusing, but we've had nothing but great food every time.