Hey you guys know what's really fun?
STATISTICS!!! 
The top two songs (three if there's a tie for second place) for each album ARE:
A Song for XX
1. A Song for XX
2. POWDER SNOW
LOVEppears
1. And Then
2. Who...
Duty
1. SURREAL
2. SCAR
I am...
1. M
2. Naturally
RAINBOW
1. HANABI
2. Free & Easy (tie)
2. Heartplace (tie)
Memorial address
1. Memorial address
2. ourselves
MY STORY
1. Moments
2. About you (tie)
3. walking proud (tie)
(miss)understood
1. alterna
2. HEAVEN
Secret
1. JEWEL
2. momentum
GUILTY
1. talkin' 2 myself
2. fated
NEXT LEVEL
1. Sparkle
2. GREEN
Rock'n'Roll Circus
1. Microphone
2. BALLAD
Love songs
1. Love song
2. Last angel
FIVE
1. BRILLANTE
2. progress
Party Queen
1. Return Road
2. Tell me why
Love again
1. Sweet scar
2. Song 4 u