The Double Unit Knot http://www.netknots.com/fishing_knots/double-uni-knot-1 is easy to tie, and is still my preferred knot to tie whilst on the water. However, the FG Knot https://www.youtube.com/watch?v=pjzUb5QRKuk has a smaller profile and travels through small guides much better, allowing for casting greater distances. In addition, it is supposed to be one of the strongest knots. I find the FG Knot more difficult to tie, particularly if you aren’t tying them often, and therefore find it better to do so in the shed, prior to venturing out to fish. There are a number of tutorials on You Tube for the FG Knot, but I find the one above the easiest to understand. The FG Knot, like most fishing knots, is more difficult on small braid/leader.
For tying hard body lures I use the Loop Knot http://www.netknots.com/fishing_knots/non-slip-loop-knot . For SP I use the Fish N Fool Knot http://www.netknots.com/fishing_knots/fish-n-fool-knot