1st Tier: Super Vegito
Ultimate Gohan
Super Saiyan 4 Gogeta
Super Saiyan 2 Goku
Gogeta
Super Buu (Super Saiyan 3 Gotanks absorbed)
Janemba
Some of the most powerful fighters in the game, and probably some of the most overused and favored.
2nd Tier: Super Saiyan 3 Goku
Majin Vegeta
Vegito
Frieza Final Form (100%)
Super Saiyan 3 Gotanks
Cell Perfect Form (100%)
Kid Buu
Future Trunks (Fighitng) (Super Saiyan)
Piccolo
Worriors that are powerful and popular in the game, but they don't quite have what it takes to make the first tier.
3rd Tier: Super Saiyan 2 Gohan
Super Saiyan Goku
Great Saiyaman
Goten
Super Saiyan Goten
Trunks (Kid)
Super Saiyan Trunks (Kid)
Gotanks
Gohan
Gohan (kid)
These characters are boarderline, they are not the best, but they are not the worst either. Fun to use if you just want to kick around.
4th Tier: Chiaotzu
Yamcha
Raditz
Saibaman
Dodoria
Burter
Recoome
Jeice
Guldo
Android #19
Cell Jr.
Android #20
Hercule
Videl
These are characters that are among the weak, some are placed in this tier either because they don't have the strength, or are unpopular or unfavored.
Others: Things I have not mentioned.
Yawn - what is there to say?