if youlike having mulyiple classes, the best advise is to do this (with the assumption that you learn to do your job somrhow along the way):

1. level a dps class via quest and storyline
2. meanwhile, lvl a tank/healer class via dungeon

because many hate lvl-ing dps classes because it's a very grindy process, and it is v hard to queue for dungeons (some of which are compulsory for storyline progression) as dps, but almost instant if you are tank/healer. of course, as tank/healer you also have to be very familiar with the mechanics of the fights, so its more effort for u.