It is difficult to answer the question of "who is right" since everyone thinks their religion is right! Answering the question of "who is orthodox?" also brings up the question of who has the right to determine what is orthodox.
(Keeping in mind many Muslims consider all Shi'is to be unorthodox!)
Anyway, as you say, many people today consider the strongly fiqh-based approach to Twelver Shi'ism (i.e. the first stream of thought, in that Shaykhism also emerges from that line) to be the "mainstream" or "orthodox" one.
It is also argued by scholars of religious history that Alawism and Alevism are heavily syncretic religions (i.e. strong mixes of Islam/Shiism and other religions). My understanding is that some Nimatullahis self-identify in this way today (that is, as strongly integrating beliefs prior to Islam), but I don't know if that reflects the whole tradition, and, in any case, just because a belief is ancient does not necessarily mean that it is wrong. However, it could be construed as "less orthodox" insofar as it there is no evidence that it comes down a direct line from the Prophet/Twelve Imams.
My impression has always been that today's Alawism and Alevism are more "cultural religions", i.e. they are practiced in some areas as local traditions but don't absorb outsiders easily.
Anyway, my view on this is, firstly, to follow the advice of Imam Ali (A) - namely, first know the truth, and then you will come to know the people who are on the truth.
Second, insofar as Islam is a scriptural religion, you can read Qur'an and hadith, especially the Qur'an, and compare the beliefs and practices of these different groups and see what seems to fit best with it.
Third, there is no harm in taking what is good from different places. If you have the option to practice Shi'ism in one or more of these interpretations, you can see what leads you to the truth, what beliefs and practices are healthy or unhealthy, which reflect the spirit of the Qur'an, what you think best reflects the intent of the Prophet (S), etc.
Lastly, of course, seek divine guidance.
Usually we already know what is true and the kernel of the answer is already in our heart, but sometimes we aren't ready to act on it yet, and we have to wait until the time when we are ready to acknowledge whatever we know is true.