Vai has a compilation called
The 7th Song that features only his ballads. I thought it was really good. But if you want a more varied look at him, I agree that Passion and Warfare is his best.
Satriani is harder. His albums are all about the same quality. I probably like Crystal Planet a bit more than his other stuff, though.
If you really like instrumental guitar hero albums, you should also check out John Petrucci's solo album,
Suspended Animation
And be sure to check out the various G3 videos if you want to see Satch and Vai in action. Each video features a few songs by both Satch and Vai and a third guitarist. Followed by a jam session featuring all 3 guitarists.
The videos are:
G3 Live in Concert (with Eric Johnson as third guitarist)
G3 Live in Denver (with Yngwie Malmsteen)
G3 Live in Tokyo (with John Petrucci)