Loop to loop here. I fish SA floating lines with factory loops and tie mono loops on the sinking lines I use that don’t have factory loops. I tried the chinese finger puzzle loops (I think by Rio) and went through 2 packs before giving up. Some suggest gluing them, but I didn’t think to try it when I was fighting them.
Simple: Leader with a perfection loop, tied to the line with a half hitch. The line already has a half-hitch prior to the leader connection.
I found this strength test on itinerant angler i thought it might be of interest
okflyfisher, thanks for this thread, it is quite timely for me. I needed to replace a worn line, and SA discontinued my old favorite, the Supra, and the only DT in their line up now comes in at a hefty $75. So I decided to try Hook and Hackle’s line in the DT5F. They are, of course, loopless, but to save $45 I can tie a couple knots. I did a “test” with the castwell knot direct to a leader loop, and I could not break the connection, as much as I tried. Despite all the endorsements, it takes a leap of faith to trust such a simple knot, but a fine film of Zap a Gap will add to my confidence. This rig is less bulkier than the nail/perfection loop I am using now, and has the added advantage of being easier to replace on stream if needed.
For more info this is a good thread also… http://www.flyanglersonline.com/bb/showthread.php?45681-Does-it-have-to-be-a-nail-knot
U
Yep…another convert! Been using that knot for years and it is hard to get anyone to believe that it will do the job, but it does. Well.
Glad you have seen the light. 
Brad
cast well knot works for me when the loop on the end of the line gives out
From my own testing:
Nothing goes through the guides like a needle nail knot with a small perfection mono loop, Whitlock’s super glue connection would also work well
The needle nail knot also recommended by some big names in the sport Gary Borger, Lance Egan , George Anderson for what that is worth. They do have lots of experience on the water
From relative strength standpoint a nail knotted fly line loop is stronger than an albright knot, an albright knot and a castwell knot are about equal strenght and a needle nail knot while fairly strong is the weakest. 30% of the needle nail knots were stronger than a castwell knot. YMMV
Each Knot has it advantages. The Castwell knot is strong the simplest of all the knots. The needle knot goes the rod guides the best, the nail knotted fly line loop is by far the strongest and it is easy to make a very small compact loopand the albright knot is strong and a knot most people are familiar with because they have used it as their fly line backing connection
I have used the castwell knot for years and it has never failed me.
Since I’m old and have fat thumbs I avoid knots whenever possible! Loop-to-loop.