The printer’s manuscript has the singular land here, which the 1920 LDS edition emended to the plural lands. Otherwise the text uses the plural lands when comparing the promised land with other lands:
Here in Ether 1:42, Oliver Cowdery could have accidentally omitted a plural s when he took down Joseph Smith’s dictation or later when he copied the text from 𝓞 into 𝓟. There is some evidence that Oliver tended to omit the plural s from lands as he copied from 𝓞 into 𝓟; in fact, in two out of three cases, he did not catch his error:
The example here in Ether 1:42 is different in that the word land(s) is postmodified by the prepositional phrase “of the earth”. There is one other example in the text of “all the land(s) of the earth”, and it has the plural lands:
There is, however, one instance where the promised land is compared to being “above all the earth”:
This example is semantically equivalent to saying that the Lord could carry them to “a land which is choice above all the land of the earth”. Note that this instance, in Ether 1:38, of “a land which is choice above all the earth” precedes Ether 1:42 by only a few verses. In other words, the use of the singular land in the earliest text for “above all the land of the earth” is possible, although we can find no explicit use elsewhere in the text of the fuller expression, “above all the land of the earth”. But since the singular will work, the critical text will restore the earliest reading here in Ether 1:42, “a land which is choice above all the land of the earth”, but with the recognition that this could be an error for “a land which is choice above all the lands of the earth”.
Summary: Restore in Ether 1:42 the earliest reading with the singular land in the relative clause “which is choice above all the land of the earth”; this reading will work, although the possibility remains that the singular land could be an error for lands (which is how the text was emended in the 1920 LDS edition).