Let me clarify . I generally drift fish jigs for chum and I seldom have a knot or leader break. I use 12lb leaders with no difficulty. When I switched to a spey rod I use loop to loop
connections using a 20lb butt section on the sink tip with a perfection loop. The leader ( 12-15 lb ) has a perfection loop as well. It was the loops on the leader that were breaking . Using a Rio braided loop on the sinktip seems to have solved the problem. Someone told me today that the perfection loop can be a weak link.
I've been into a fair # of chum on my 8wt spey the last week or so. I'll tell you what I do and I never (well almost never) have issues with knots busting.
My sink tip has a factory loop on it. I use the RIO MOW tips. I take a piece (2-3 feet) of 15lb Maxima UG and tie a loop on the end so I can loop-to-loop it to my sink tip. I've tried the perfection loop and found it a pain to tie. I just use the one that is two overhand knots...I think called a surgeon's loop
I've never this knot bust. From here I tie in 2-3 feet of tippet. Usually 10 or 12 lb UG. I use a double surgeon's knot. If fishing lighter line than this for trout I'll go tripple S.
I find a blood knot connection just as reliable but much harder to tie on the river esp with cold hands.
With some other btands of mono maybe 20lb would be better looped to the sink tip, but I find UG pretty thick for its rating and I havent had 15lb cut through my tip loop yet and I've had to snap off the odd foul hooked chum or humpy.
IMO connecting mono to flouro with whatever knot is asking for a break. With loop-to-loop maybe not an issue. When I have had knots bust it has been connecting M to F with a blood knot or surgeon's knot. Maybe it depends on the brand/quality of the M and F? I've had no issues with F to F or M to M.
Also IMO flouro totally unecessary for chum. They are not leader shy. People say it is more abrasion resistant and sinks better. I personally have not noticed I catch any more fish with F than M. I just like good old UG and sue it for most of my leaders for salmon and trout. The odd time if I'm into some really picky coho I'll break out the spool of 6 or 8lb expensive Seaguar flouro. Honestly I don't think it makes a diff but it gives me a bit more confidence.