I use a simple clinch knot with fluoro. In the lighter tests, it can fail if you don't seat it properly. If I'm making leaders up ahead of time, I just put a drop of superglue on the knot. The polamar knot is a good choice with lighter tests, but can be a bit bulky. I use a surgeon's end loop on the other end to make leader changes easy.
I like Seaguar best.
Hope that helps.
-jon