I like the Mediaeval Baebes and have some of their CDs. They are fine musicians, though if I have one tiny criticism, it's that they're just a teeny bit too sweet at times.
When it comes to interpretations of mediaeval music I must say that there are people that I now prefer. Blackmore's Night, for example, who mix their own original songs with mediaeval themes- a little bit twee at times but great musicians and very exciting. Then there's Maggie Sand who combines mediaeval tunes with trad. songs- anachronistic maybe, but she and her band do it so well. My current faves are Circulus, although they probably don't classify as folk and you wouldn't see them on the folk circuit, I love the way they blend folky-prog-rock with mediaeval themes.
What all four have in common, imo, is that they render mediaeval music in a way that, though it may not be authentic (though who knows what "authentic" would be in this case?) is musical and, I think, in the right spirit.