If you are going to attach two pieces of line, rope, string, etc., the best knots, IMO, are normally those that are likely to jam; i.e. you will not be able to untie them easily if at all. I prefer using a double becket bend, see: http://www.tpub.com/content/administration/14067/css/14067_57.htm, because it is very secure. You probably would not tie a knot like the fisherman's or becket bend, unless you were joining two different pieces of line together. It could be done because the one you have is too short or when tying a fishing line to a leader, etc. If you do need to cut one of these knots, cut the loops that you made around the standing parts, which should help you save more length from the line.

As far as the ultimate knot, that title belongs to, has always belonged to, and will always belong to the bowline. IMO, one should know how to tie a bowline with your eyes closed.