[Koha] Z39.50 servers

Hi, All: We're a small rural public library automating for the first time with Koha/ LibLime and we're looking for advice on your favorite sources for copy cataloging. We have quite a backlog of uncataloged items to get through. Koha's default search targets for us are FirstSearch WorldCat, LOC, New York University, New York Public Library, Columbia, & the Smithsonian Institution. Anyone have opinions, strong or otherwise, about their relative merits, or suggestions for alternative preferred servers? Many thanks, Cab Vinton Sanbornton Public Library Sanbornton, NH