I think each one is a favorite, but for different reasons.
My first quilt, because I got it finished (9 patch, hand pieced both sides, hand quilted)
My paper pieced halloween cat, because I learned paper piecing
My heart bargello, because I designed it, and made it for my parents' 60th anniversary
My lone star, because I learned about doing them with strip piecing, and it worked out well
The Volkswagen quilt I designed and made for my nephew's wedding
My rainbow quilt because I learned how to dye the fabrics, and the quilt shows them off.
The table topper I made last week because I learned something new.