I go with the most recent Tolkien statement; that Orcs are twisted and corrupted Elves and later men-(and perhaps Hobbits?)
Hello and welcome. About the matter of most recent, I don't know that that's necessarily Tolkien's most recent statement about the origin of orcs; and the Silmarillion is a compilation made by Christopher Tolkien and Guy Kay, and does not include [nor was intended to always include] Tolkien's most recent descriptions or statements about a given matter.
In my opinion the best bet for Tolkien's most recent idea is: Orcs from Men, some Maiar among them [noting that Tolkien himself altered the timeline to make this possible]. Christopher Tolkien presents the Orcs from Men text, and comments...
'This then, as it may appear, was my father's final view of the question: Orcs were bred from Men, and if 'the conception in mind of the Orcs may go far back into the night of Melkor's thought' it was Sauron who, during the ages of Melkor's captivity in Aman, brought into being the black armies that were available to his Master when he returned.'
'But, as always, it is not quite so simple. Accompanying one copy of the typescript of this essay are some pages in manuscript for which my father used the blank reverse sides of papers provided by the publishers dated 10 November 1969. These pages carry two notes on the 'Orcs' essay: one, discussing the spelling of the word Orc, is given on p. 422; the other is a note arising from something in the essay which is not indicated, but which is obviously the passage on p. 417 discussing the puppet-like nature inevitable in creatures brought into being by one of the great Powers themselves: the note was intended to stand in relation to the words 'But the Orcs were not of this kind'.
Christopher Tolkien, commentary, Morgoth's Ring
So, in what way do these two notes complicate Tolkien's 'final' view of the matter? I looked at this question earlier in this thread, and here's what I came up with anyway...
1) one of these notes carries a statement that denies an essential conception found in the text on Orcs from Men, and the denial hails from the detail that this later note suggests Morgoth had great numbers of Orcs at the height of his power and still after his return from captivity.
So the 'denial' is that in the Orcs from Men text, Morgoth had a great number of Orcs after his return from captivity, not before. And to muddy things further here, this may be a draft version for a variant passage that does not include this detail!
2) this short note concerns the spelling of the word orc: here Tolkien notes that he will spell it ork, just as he had noted in text IX, where Orcs were from Elves [and 'probably later also of Men'].
I think Christopher Tolkien's point with these notes is that they might throw some measure of doubt upon the seemingly 'final' idea that 'regular Orcs' were bred from Men (text X). That said, there is another late text which appears to have Elves stating that Men are the source for Orcs:
Late text (lacks date other than final period of Tolkien's writings): author's note (note 5) to The Druedain:
'To the unfriendly who, not knowing them well, declared that Morgoth must have bred the Orcs from such a stock the Eldar answered: 'Doubtless Morgoth, since he can make no living thing, bred Orcs from various kinds of Men, but the Druedain must have escaped his shadow;...'
I can't really tell if this description is later or earlier than the two notes dated 1969 or later, but again, if I had to bet money, I would say Orcs from Men is the latest idea -- as we can't really be sure if the seeming denial of the first note means that the whole idea of Orcs from Men was discarded...
... and I think the spelling of ork instead of orc need not mean that the idea of Orcs from Men was necessarily superseded, simply because the spelling of ork can also be found in an earlier text where Elves were included -- nor does Christopher Tolkien propose that the idea was certainly discarded in my opinion, as to my mind he is rather pointing out, as he says...
... 'it is not quite so simple'