Starting out most MMO's the rule of thumb. Is get the trade skills people need. And go after the classes most used. These are usually the tank and healer classes. Also anyone who can hybrid those roles work as well.
Vanguard= Vanguard maybe the best thing to pick. The reason being not many people make tanks on purpose. And it's not too glamorous.
Spirit Shaper= Healer! of course, this would be second on the list. The reason it's not first is because in this game it is glamorous and cute. So theirs really not a shortage of them.
Occultist= The resident dps slash healer class. This is third because it has a popular emo look. Very flashy skills plus it can fill 3 roles. Crowd control, Dps, Healer.
Swordmaster= Gets fourth because it can do both dps and tank. Takes a bit of skill to tank and you can light crowd control. I wouldn't rely on this too long though.
Swordmage= This is a pure dps class in a bad place. It looks cool but unless its a range fight you don't need them much.
Gunslinger= Has the same issues a bit more tanky than Sword Mage. But still suffers the same fate.