If you think you are going to major in economics, look at the course catalog and map out what you’d take (including the distribution requirements ) at each. See if there’s a meaningful difference to you. I don’t think one is “better” and I think you’ll have the same kind of interactions with profs at both. I know the econ program at Colby is good.
Think about the environment. Colby is remote, so a very self-contained community and lots of kids do outdoorsy activities for fun. Haverford is in a suburb of Philly with easy access to the city. If your idea of fun is going to the city to listen to music or visit a museum or if it’s snowshoeing in a national park, that might point you to one over the other.
I personally like Jan Plan (although I wouldn’t choose specifically for that.) But if you’re on the fence, consider it. It lends itself to studying things that might be tricky during a regular term, either because travel is involved, or it’s something that requires a lot of work with others (a theater or music project, for example ) that would be a scheduling nightmare during the regular term.
Both are wonderful schools and regardless of the choice you make, it’ll be a good one.