This will just get super confusing as we go on, so I just made these.

Beginning Gohan (injured): 100,000,000

Season 1 Gohan: 410,000,000
(Super Saiyan): 20,500,000,000
(Super Saiyan 2): 41,000,000,000

Season 2 Gohan: 450,000,000
(Super Saiyan): 22,500,000,000
(Super Saiyan 2): 45,000,000,000

Season 3 Gohan: 600,000,000
(Super Saiyan): 30,000,000,000
(Super Saiyan 2): 60,000,000,000

Season 4 Gohan: 798,000,000
(Super Saiyan): 39,900,000,000
(Super Saiyan 2): 79,800,000,000

Gohan (usually suppressed): 5,000

Goku (Season 2): 500,000,000
(Super Saiyan): 25,000,000,000
(Super Saiyan 2): 50,000,000,000

Nightmare Moon: 90,000,000

Discord: 350,000,000

Chrysalis: 120,000,000

Changeling: 20

Elements of Harmony: 700,000,000

Celestia: 85,000,000

Luna: 80,000,000

Cadence: 70,000,000

Twilight (unicorn): 500
(EG): 3
[alicorn (learning)]: 1,500,000

Rainbow Dash: 150
(training): 250
(EG): 20

Applejack: 200
(EG): 30

Rarity: 40
(EG): 5

Pinkie Pie: 139
(EG): 18

Fluttershy: 20
(training) 30
(EG): 5

Sunset Shimmer: 300
(EG): 7
(transformed): 750,000,000

Author's Notes:

If there's any other one you'd like to know, just comment.