Here, in the Omaha, NE area, it's hands-down the Country Sampler for me. In Lincoln, NE it's the Cosmic Cow.
If you're in Lincoln, Nebraska you MUST stop in and visit the International Quilt Museum. It is AMAZING and it rivals a Smithsonian musuem exhibit. Make it a day and visit the Cosmic Cow quilt shop, just two miles from the museum. I live in the Omaha area, which is 45 miles from Lincoln, and the Country Sampler has wonderful staff, the best fabric, and tons of wonderful classes.