The blues scale is probably the most important scale in rock music. When you bend the notes in the blues scale and use some vibrato, you can get the sounds of some of the greatest rock guitar players. Listen to Jimi Hendrix, Jimmy Page, Eric Clapton or even Angus Young and you will hear that most of their leads use the blues scale.
The blues scale is the easiest scale to use when you play leads because it sounds good with just about everything. The blues scale is usually played over a song where a minor chord is the tone center. But, the blues scale can sometimes even be played over a song with a major chord as the tone center.
The country scale can be combined with the blues scale to get what is called Major Blues. The Major Blues has a major chord as the tone center. A good rule of thumb is to play the country scale over the tone center, and you can mix in some blues licks over the other chords in the progression. There are no rules in blues or rock, just play what sounds good.