I'm not a polytheist. For what seems most of my life, however, I've heard and read that monotheism is in some sense superior to polytheism. This is not unusual given my Catholic upbringing, I suppose (or perhaps not--more on that later).
Polytheism has been equated with paganism and idolatry. It has been characterized as a religious belief system of a primitive and superstitious nature, replete with magic. Well and good, perhaps, for the unsophisticated of ancient times and even in modern times in savage lands, until assorted missionaries brought with them the truth and began inviting the savages ever so gently to accept it. Monotheism, though, is considered a sophisticated and far more profound system of religious belief.
Why is this the case, though? Let us acknowledge as we must that Christianity, and especially Catholic and Orthodox Christianity, has certain problems in claiming to be monotheistic. The first problem is the Trinity. It may be a great and unfathomable mystery, but on its face, at least, it requires one to maintain that a single God consists of three persons, each of them God but all of them God, as well, and necessarily so. It should surprise no one that such a conception of God is not easily accepted as monotheism.
Then there is the related problem of God having a son (or indeed being the Son, as well as the Father and the Holy Spirit). The pagan gods had sons; plenty of them, in fact. Those sons, however, were distinguishable from their divine parents, and so it may be claimed that Christ as Son is not similar to pagan sons of gods; but again it must be acknowledged that this distinction that is not a clear distinction (Son of God but also God) leaves one feeling rather uneasy. Monotheism? Well, so we have been taught.
Also, Christianity's assimilation of pagan gods in the form of saints, and the prevalence of statutes and icons in Catholic and Orthodox branches of Christianity, at least, makes one wonder about the extent to which Christianity represents monotheism. Ancient Greco-Roman paganism accepted that there were minor gods subservient to Zeus or Jupiter, and the saints hold similar subservient status and have been said to perform miracles which duplicate or are similar to the works of minor gods worshipped in antiquity. It almost seems Christianity is polytheistic in a sense.
The same cannot necessarily be said of the other Western monotheisms such as Islam and Judaism. However, those religions seem to recognize angels as subservient powers sometimes involved in the interrelations between God and humanity. And we have not even considered the devil and his host of demons who seem to figure in each of the major Western monotheistic beliefs. Monotheism, it seems, still contemplates a rather crowded universe filled with supernatural powers, some good and some bad. As understood in the major Western religions, it seems monotheism may not be as different from polytheism as we have believed.
There is a least one clear difference between ancient polytheism and institutionalized monotheism, though. The major Western monotheistic religions each claim that the god they worship is the only true god, and that the worship of that only god is the only way to truth and salvation. Ancient polytheism by its nature didn't require a belief in one god to the exclusion of any other.
The monotheism we know has been exclusive and intolerant to varying degrees throughout its history, sometimes violently so. The violence continues, and it's likely it always will as long as monotheists insist there is only one god, one truth. The superiority of monotheism over polytheism is not clear at all in this respect, to me at least. Worship of a god which requires intolerance of other religious view doesn't strike me as a religious belief, or a god, which can be called superior to much of anything.
But there have been kinds of monotheism which have not been exclusive and intolerant. Those monotheisms relate to gods who are generally less personal and less lawgivers than those of the institutional religions. Deists, pantheists may posit the existence of a single god, but not one who is so insistent on certain conduct and ceremony; a god that is less human, shall we say.
Is monotheism of this kind superior to polytheism? Well, the gods of ancient polytheism were notoriously human in nature, and as it seems that such very human gods would not be expected to hold sway throughout the universe, an impersonal single god would appear to be a more reasonable hypothesis. May their be an impersonal polytheism? An interesting question. I can't see how this would be an impossibility, though. If it's not, why would monotheism of that kind be superior to polytheism of that kind?
Would Occam's Razor make the single god preferable in that case? Perhaps. But it's not clear to me that preferable in this sense is superior. I doubt an atheist would be impressed by either monotheism of polytheism.