Sorcery is just pure Inorganic intent, it walks a separate path from Humanity, it serves our Inorganic side only. For some people, Sorcery is an appropriate path, and if it is, deluding ones self into thinking that it isn't can only make your life harder.
With Nagualism, the Inorganic side of us enlists the aid of our Human side in order to benefit the awareness of both, especially after death. Nagualism invites our Human side to take a journey into the unknown which is almost equivalent to the path of Sorcery, its for people that lean more toward their Inorganic side but not completely.
Shamanism is for people who are primarily concerned with Human affairs while alive, who use Inorganic energy to assist them in a significant but limited way. It is not in the Shaman's interest to take Inorganic journeys into the unknown to bolster his or her non-Human awareness, since they would then become less concerned with Human goals and not be able to their job as well.
It may sound silly to think that anyone would seek the assistance of Inorganic beings in matters of such things as fertility, healing and fortune, but, surprisingly, the Inorganic beings from the deeper realms are of some value here. The picture below is actually more representative of Shamanism than not, since the intent of Shamanism is guided by the desires of Man. For this reason, Shamanism will always be the most popular of the three, by far.

shamanism here I come!