I always like my fly line to leader junction to go through my guides as smoothly as possibly regardless of the technique I'm using. However, it becomes critical when Euro-nymphing because the junction slides through your guides on every cast. Loop to loops are horrific at going through guides. Nail knots are better and super glue splices are the cat's meow if you have a braided core fly line. But what do you do if your fly line has a monofilament core such as the Cortland Competition Nymph Lines I sell on the site? For me the easiest solution is a blood knot. To show you how I do this I created a quick tutorial that should get you through it pretty easily. Sorry I don't have Gilbert Rowley's filming skills!
Devin