Merida was one of my boys' favorite character interactions. The waiting area has coloring pages for the kids, so the adults can wait while the kids play, and they can shoot an arrow after. I don't think Merida is usually a big rope drop draw, so you should be able to get through fairly quickly.
Merida is my favorite princess meet and greet. There are activities for the kids (coloring pages, pretend archery) and Merida is very friendly and interactive.