For me, the harp work of Voorhees wins, but the dulcimer-guitar duo is also very pleasant. The overblown accordian work doesn't fit my image of O'Carolan's music. The duo guitar work doesn't really compare because it is an adaptation that departs from O'Carolan's line, especially in other parts of the adaptation.
(The duet on dulcimer and guitar caused "Illegal Operation" and close-down on Netscape, but worked with Internet Explorer. Had this happen before.)
We only have one basic line of any of O'Carolan's pieces, so we really know very little of what he was striving for in his music. No harmony, no grace notes, nada.