If you already have a machine dedicated to piecing, I would personally get the Tiara. Much wider harp space than the Crescendo and a larger table to support the quilt. I've test driven the Tiara and loved it!
however ... if you want to be able to have a 2nd "backup" piecing machine then the Crescendo would be a wise choice.
BUT ... by all means ... TRY them both and see how you like them!!