Playing notes from the major pentatonic over a major key and playing notes from the minor pentatonic over a minor key will always be pleasing to the ear.
In many cases you can use the minor pentatonic scale in a major key, too.
Many times though, a song in a major key can have soloing from both the pentatonic major and minor scales.
If you are playing a song in a minor key (Examples: Em, Am, Bm) then you’ll
want to stick with the minor pentatonic that matches the name of the key.
For example, if the song is in Em, you’ll want to play from the E pentatonic minor.
Whereas a song in a major key, you can use either the pentatonic major or the pentatonic minor, or both to solo with. Whatever scale you choose to solo with will be your own decision. So how do you decide which scale to use?
Well first, you’ve got to know what each scale sounds like over a song in a major key.
Examples
Here is a clip of a song in the key of E. I’m using the E pentatonic major to improvise a solo over it:
Here is a clip of the same song, but instead of the E pentatonic major scale I’m using the E pentatonic minor:
Can you tell the difference? Each has its own sound. Oftentimes the pentatonic minor in a major key has a “bluesy” sound to it.