Both are excellent knives, so either way you can't really go wrong. Both offer super slicing ability, by virtue of their flat ground blades. The differences are size, weight, feel, steel, and carry mode. While the Calypso Jr. is larger, it is also lighter, so the choice there becomes one of less bulk versus less weight. I strongly favor the fish scale textured FRN on the Calypso Jr over the smooth steel of the SS D'fly, but this is mostly a matter of taste. If you strongly prefer one carry mode over the other, then you may want to base your choice on that. If you favor tip up, go with the Dragonfly. If tip down is your preference, go with the Calypso Jr. Some will say the VG-10 makes the Calypso Jr. a better choice, but personally (although I often carry a Calypso Jr. and rarely carry any of my D'flys) I find ATS55 easier to maintain. Of course, if you are left handed, then the ambidextrous clip on the Calypso Jr. would becomes a major plus for it. I personally prefer the way the larger handle of the Calypso Jr feels in my hand, and its light weight just adds to its appeal to me.