Album 1 is the first volume in the Pray Twice series. This album focusses on songs that are "worship" focused. Most of these are appropriate for singing in a group setting with other people, to worship God. Some may be reserved for personal prayer, such as You're God, I'm Not.
Album 2 in the Pray Twice series focusses on songs that are appropriate for personal prayer.
Album 3 has a good blend of songs that are appropriate for worship settings and / or personal prayer. Some are situational songs. Of course, all songs can be used in personal prayer; that's how they were composed!