By far
Definition 1 of 1
Pro Tip 1/3Extremity Emphasis
Use 'by far' when you want to highlight something as much more extreme than others in its category. 
His solution was by far the most effective we've seen.
Pro Tip 2/3Comparison Required
'By far' needs a comparison; it doesn't work alone to describe a single item without context. 
That movie was by far the worst this year.
Pro Tip 3/3Positive or Negative
The phrase can describe both good and bad extremes; context determines the meaning. 
This is by far the least expensive option.