I’ve had little (really no) success with yDNA testing. I have one match with my surname (a person I know and who tested at my suggestion). Otherwise the matches are with random surnames. I had hoped to find that my people were a branch of a more common Irish line (like O’Neill, O’Connor or the likes). There is no pattern to the names that matched.
Autosomal was altogether different. We got a few strategically placed family members to test so that we could determine on which side of the family a match most likely connected. We made contact with a descendant of my great-granduncle, of whom I had no record till the match. The relevant parish register starts far too late, but other records provided the evidence that this man was indeed my great-grandmother’s brother.
Then there was a match with someone who had my great-great-grandparents as their ancestors. They were descended from a daughter named Julia and I had no record of her. True enough, when I investigated it Julia was indeed a daughter. Julia’s mother had an extremely rare surname that I’ve been wondering about for years. The Autosomal matches include two separate people who have that surname in their trees, so Autosomal DNA has opened new vistas for my ancestral research.