Neddle Knot or Nail/Tube Knot; they are all tension knots and work great, been using them for about 17 years. Needle Knot is a great one as well but it is the second half of the knot(which happens to be the Nail/Tube knot) that holds the structual integrity and also allows for a clean transfer of the kenitic energy in the fly line.

Nail/Tube knot can easily be performed on the river and with no tools while replacing leader. Needle Knot is much cleaner but requires the use of a tool.

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Best Regards