Stringsinger,I have also tried many different grips,but am now most comfortable with the classical grip[I think the most important aspect of this is the bent thumb].
perhaps, how you feel most comfortable is important,or if you have a definite idea of playing one kind of music[eg old timey]adopt a grip up the bow,the only problem with this that if you want to then play texas long bow style or bluegrass,its arguably not the best grip.
the other grip I like is holding the bow under the frog,the disadvantage I found with this was that I [probably just me]couldnt get so much pressure on the top of the bow with the index finger.
I do believe that a CLASSICAL grip with bent thumb is best,because you should have no problem playing every kind of music with this grip, with a classical grip with fingers at the frog end the player should be able to execute short bows ,long bows ,and play every kind of music and every kind of Irish music from sliabh lucra LONG BOW STYLE[Julia Clifford]to Donegal style.