There's sadly not 10 duets between Kurt and Rachel, but I really wanna rank them anyways, so I'm going to.
And my ranking of the eight Rachel/Kurt duets are as followed:
8
Song: Bring Him Home
Season: Four
Episode: Diva
7
Song: Don't Cry For Me Argentina
Season: Two
Episode: Special Education
6
Song: Happy Days Are Here Again/Get Happy
Season: Two
Episode: Duets
5
Song: Ding-Dong! The Witch Is Dead
Season: Three
Episode: The Purple Piano Project
4
Song: Get Back
Season: Five
Episode: Tina In The Sky With Diamonds
3
Song: For Good
Season: Two
Episode: New York
2
Song: Popular
Season: Six
Episode: 2009
1
Song: Defying Gravity
Season: One
Episode: Wheels