It would be between them, Leona, and Kelly Clarkson I'd imagine.
1D definitely did well though considering they were not even in the top 10 best vocalists of their series of TXF imo.
And I have watched the performances of that year back recently so I am looking at them through a fresh lense rather than a possible bitter one from when I was 13.
Out of interest how have they all been doing as soloists lately? I know that Harry and Zayn got off to good starts initially, but I haven't heard anything since.