I do Kayak.com. But the trick I have learned is check to booking individual legs separately. Some airline groups don't seem to play well with others. Especially to South America with Copa Airlines, I booked separate legs and saved $2K over search engines that don't seem fully integrated.
I just checked for a flight I need to get back from Ireland and Kayak was better by far with the exception of one flight on skyscanner which had 3 stops. Would save $200 pp but add two stops and 8 hours to the day. (Dublin to Toronto to NY to Norfolk) My wife would probably kill me by NY
(and at that point I probably wouldn't care.)
But I bookmarked skyscanner and will check it again ...... never can tell.