As treefall said, bards are an incredibly versatile class. I use whatever songs best fit my purpose at the time. I've been known on occasion to still use the L1 Chant of Battle all the way up to the L60 group DA song. Even Hymn of Restoration has better HP regen than Cantana, so I've been known to whip that song out at L60.
Use the wiki to read all the song descriptions:
http://wiki.project1999.org/index.php/Bard
Use this google doc to calculate buffs/debuffs based on level:
http://www.project1999.org/forums/sh...ad.php?t=50223
Know what role you are trying to fulfill:
Puller
Resists
Haste
STR
DR
MR/FR/CR Debuff
Slower
CC
DoT
AoE
Mana-battery
Movement
(not inclusive)
...and/or any combination of the above.
Pick your songs based on that information.