I do not like any of the various ways one can connect one continuous sheet to the headsail (i.e., cow hitch) as that does not allow me to turn my sheets end-for-end to avoid chafe in various locations and lengthen the usefull life of the sheet. While the constrictor and buntline hitch are great knots, they are near impossible to untie once set and stressed. I also would not recommend the use of any kind of shackle to connect sheets to headsails. One bonk on the head and you'll know why....
I suggest continued use of the ever-faithful and wonderful bowline.
It's easy.. Start out with cows hitch/larks head and when the line wears cut it and end for end and use bowlines or a buntline that won't "shake loose"...
Buntlines are easier to tie for the less knot inclined..
I too have used bowlines for years, my father and grand father used them too. In 30+ years and thousands of miles never had one shake loose and don't recall that my grand father had any shake loose either but I never asked. He was the type though who would stop doing something at the mere hint of failure. I guess bowlines worked ok for him. I don't doubt that they could shake loose but I know lots of cruisers and sailors who have used them for a long time with good success.
I even sailed through a very well known storm in the fall of 1991 on a vessel with bowlines on jib sheets. Also sailed the 1979 Marion to Bermuda on a schooner using lots of bowlines, and that race was nasty! They are far from perfect as I have had then snag and they do weigh more in light air than larks head but shake loose, not yet, and still waiting for that to happen to me.
I am currently running bowlines but only because I got a very good deal on some cut ends that were only long enough for individual sheets but not long enough for one continuous.
My preference is a cows hitch / larks head but I don't get too worried if I use bowlines as my own long personal history is enough evidence for me that they hold up well. I have used buntlines too, great knots, but they don't like to come undone..
A friend used a variation of the constrictor on a single sheet and was unable to get it undone and had to cut the sheets. Not a problem he still used them and had an opportunity to end over end them. Constrictor is NOT going to slip nor come undone very easily.
I have seen a larks head slip but it was on a ring and the line was brand new so perhaps not tight yet but I have used them a lot and raced on many boats with them and have not seen slipping as an issue. Plenty of good ways to attach a jib sheet and it comes down to personal preference like most anything..
Interestingly enough I understand that "virtually NO ONE will recommend them ..." but the first book I grabbed off the book shelf......
Of course most books disagree with each otehr on many issues so choose your own knot that you feel comfortable with..
US Sailing The Certification Series - Basic Keel Boat - Pg. 30
"Secure the jib sheets to the clew of the jib using bowline knots."