I think the coolest thing about JK3 Modeling is that I've seen so many custom models for this game ported for mods in other games, especially models by NeoMarz1 and Hapslash
Valve HAD JA beat in moddability UNTIL the source code for JA was released. JA is much easier to mod. The drag and drop PK3 system is hard to beat as far as modularity of the game.