Just make both,I know I will . It stands to reason clerics will be the most powerful healers ( unless NCsoft doesn't design the class right ) but I think chanters will by far be the best buffers .
I never - in any MMO- just level one character but several at same time . When you want to beat the c**p out of everything you load up your assasin and when you feeel like being supportive you play with your cleric/chanter
I like the idea of chanters being somewhat similar to WoW-druids but Blizzard designed druids so they were good at everything but great at nothing. Don't want that for chanters : let them be really great at buffing and still be able to do some damage so you can at the very least level the class without having to rely on others
for everything ( same applies to clerics, hope you are not forced to group for even the earliest quests )