I don't think it matters all that much for larger patterns and bass type fishing.
For smaller patterns and trout (and other "smart" fish), I use 4x or 5x with
good results. I'll occassionally use 6x for stuff smaller than a #14 dry. I think
having the leader on top of the water might be better than having it a few inches below, unless it becomes invisible below. I dunno....Isaac Walton used
horse hair tippets
I've been tying my own leaders for several years now, and Orvis SS mono works well for me.