Ault is good, both his 16th and 17th century ones (I've only recently been able to acquire my own copy of the latter). Quiller Gouch, I have but have little use for, because with Child it's unnecessary, and when it comes to traditional songs beware of editors who weren't collectors- you'll usually get a conflated text rather than a true traditional one. They are good songs, but if they aren't the way any traditional singer actaully sang it, then they aren't folk songs as far as I'm concerned.
Hampden I don't know. Barclay Squire: I only know of his collaborative one with Lucy Broadwood, and co-editorship of the Fitzwilliam Virginal Book. I had only a mistaken reference to his index of ballad opera tunes which I coundn't find, so started my own, and am glad I did, because when I finally located his I found mine was much better. {I didn't find out about the good one in 'The National Tune Index', 1980, until much later.)