I leveled a Sage to 50 through quests,
then I did it with a Commando only with pvp,
Assault Spec on the low level bracket is really good, too bad commandos suck at lv50 pvp
I was luck I had armormech on him so I could keep my companions gear updated, class quests become really difficult if you dont upgrade your companion gear
and now that I finished getting my PT tank through quests to 50,
I'm doing it with my Assassin, lv30 so far
again, synthweaving from my sage was crucial to keep companion gear updated
it isn't that bad, it takes a lot more time to get to 50, even with the 30% legacy boost, but it i much more fun than having to do those 4 stage bonus quests all the time