It really depends on what you're looking for - a buffet with characters or a calm lunch in a cozy restaurant. Pick your experience then pick your restaurant.
We just ate at both places during our last trip and both were absolutely delicious!! It really just depends what kind of food and atmosphere you are looking for. Crystal Palace has more variety since it is a buffet, but it can be noisy at times since there are characters. Liberty Tree Tavern has more homestyle food (the Pilgrims' Feast is excellent, as is the Ooey Gooey Toffee Cake) with a quieter atmosphere. If you aren't on the dining plan and cost is a factor you may want to go with LTT, since CP is a buffet with a fixed price. I'm sure you will enjoy either restaurant and will have an amazing lunch!