Three things. First, finger choils have totally spoiled me. They give you an excellect grip on the knife _right_down_thre_ where you really need it--next to the blade. For some time now I've carried mainly the Calypso Jr, Military, and Paramilitary, all of which have finger choils, and I love it. Small difference, but worth it to me.
Second, the clip is better mounted on the handle. Although nobody else seems to talk about it, I've never seen an FRN-handled, barrel-screwed knife (like the Delica, Endura, and Native) that wasn't "distressed" at the screw from the clip getting torqued. I'm not a big fan of the barrel screw. The tree-screw mounting on the Calypso Jr. is a big step up, IMO, and I've given one as a gift for just that reason. (It's embarassing to tell somebody "this is a Spyderco; it's a solid, well-made work knife that'll hold up much better than the flea-market knives you're used to", only to have to explain a month later that no, there's no way to fix the clip mounting that just gave way like play-dough)
It's also prettier than the Delica, IMO.
But those are little things, that may matter much more to me than to you. The _big_ reason most of us love the Calypso Jr. is the full-flat-grind. The Delica is a wonderful cutter; everytime I see how thick the average "tactical" knife is, I treasure my Delica even more. But it's hard to beat the cardboard-eating power of that thin, flat-ground VG-10 blade. And the Calypso's tip is amazingly thin. It'll snap right off if you don't use it correctly, but if you _do_ use it correctly, it'll probably outcut anything you've ever used (outside of a boxcutter, that is...)