It's a preference, but drop in bobbins (horizontal bobbin systems) are known to have more tension issues because of the extra 's' curve the thread has to pass through. Vertical type bobbin cases are preferred by many quilters because of this. I have both drop in bobbin systems and vertical types and the vertical type does tend to give consistently better stitching and tension. But, I have drop in Elnas and Janomes and love them too.