I like all the partners so far, but I kind of feel like D-Walker is the biggest novelty unit among the four. D-Horse is fast, can travel a good chunk of terrain and you can actually stealth a little better with him because enemies don't think twice about seeing a horse as they do the Walker units. D-D is all kinds of awesome and the best scouting unit of the four. Quiet is awesome for having a practical backup and is a decent scout in her own right. I haven't quite found D-Walker's niche among the three besides maybe assault, which is not a play style I use too often in these games.