Is there a preferred spelling for the word "leaderboard"? Should it be one word or two? It would seem that both are correct, but is either preferred?
If I look up leaderboard as one word in OED, it returns a reference to leader board as two words, which I suppose says something about which they think is correct!
Searching the corpora yields 13 instances without a space in the British National Corpus (BNC) against nine with a space; and in the Corpus of Contemporary American English (COCA) it's 82 without versus 90 with. [I think; I'm not all that familiar with those tools]
I would say those results are inconclusive.