Read Denver Snuffer's argument for Nephi, which I find highly useful and persuasive:
If Joseph identified the angel who visited him in September 1823 by the name “Nephi” throughout his life, using it in three drafts of his history, using it in the newspaper he edited, and not changing when given many opportunities to do so, the conclusion it was a “clerical error” that was corrected by “an unknown hand” is at best insufficient.
And, here's the thing:
The identity of the angel really does matter.
Think about it: Even if Joseph Smith made all of it up, we ought to give him the benefit of the doubt concerning the existence of some plan, some schema as he put his mythos together.
Moroni is the last prophet to possess the plates, and he buried them, so that makes him an attractive candidate for the identity of the angel who passed his charge over to Joseph as the artifacts' new steward.
But Nephi was the person who gathered the artifacts, the person most responsible for putting the collection together. Indeed, it would also be correct to say that the plates were part of the royal relics of the Nephite Dynasty, at the head of which King Nephi stood:
2 Nephi 5:18 wrote:And it came to pass that they would that I should be their king. But I, Nephi, was desirous that they should have no king; nevertheless, I did for them according to that which was in my power.
King Nephi's dynasty was given America as his land, so both the relics of his reign and the dominion he was given were his to pass along to the new Josephite king in America: Joseph Smith, Jr.
Now, you may be thinking, "WTF, dude?!?!?!?" Josephite king in America?
In this regard, consider the letter of Joseph Smith' Jr.'s cousin, Jesse Smith, of 17 June 1829:
Jesse Smith wrote:he writes that the Angel of the Lord has revealed to him the hidden treasures of wisdom & knowledge, even divine revelation, which has lain in the bowels of the earth for thousands of years [and] is at last made known to him, he says he has eyes to see things that are not, and then has the audacity to say they are; And this Angel of the Lord (Devil it should be) has put me in possession of great wealth, gold and silver and precious stones so that I shall have the dominion in all the land of Palmyra.
So the angel, who, as Denver Snuffer demonstrates is Nephi, shows Joseph Smith where "treasures of wisdom & knowledge, even divine revelation" are buried, and, moreover, "put into [his] possession great wealth... so that [he would] have the dominion in all the land of Palmyra."
Joseph Smith is being given a kingdom by the land's former king. The location of the relics in the Hill Cumorah in the vicinity of Palmyra is absolutely key. The "Two Cumorahs Theory" is completely nonsense. The royal relics of the Nephite Dynasty were buried near the capital of Joseph Smith's future kingdom (as he conceived of it at the time).
This is why the identity of the angel really does matter. Sure, it would make sense for the last possessor of the relics to hand them off to their new owner. But, it seems that Joseph Smith had something a little more suggestive and potent in mind. In his mind, Nephi, the king of the Land of Promise, is handing off his sacred, royal relics to Joseph Smith, who, as their new possessor, will have "dominion in the land of Palmyra."