In my opinion newbies should avoid classes that need resource to use most of it’s skills:
Sapper, Wugushi, Inquisitor, Sorcerer, Retiarius, Chrono, Onmyoji, Enchanter, Taoist and Dievdirbys. (i’ve never played some classes like chaplain or fletcher so i won’t talk about them). The cost to use these are very high and it is better if they are your second or third class choice when you can afford it $$$.
Full support classes are not very good at the beginning neither: Kabbalist, Oracle, Alchemist, Chrono, Squire, Thaumaturge and Enchanter. They have no damage skill at all, very bad ones or trick ones to use. If you don’t mind relying on auto attack or your base class skills, you might want to start with these.
Also Exorcist is very dependent on atributes and you can only unlock them at high levels. So newbies might want to avoid this one too. I’m using one at level 180 and damage is awful.
Hidden classes can’t be the first class option so we skip them
Classes with Pet: if you have a pet/can afford one go for it but if you don’t: stay away. They won’t work without a pet. That includes: Cataphract, Lancer, Hackapell, Schwarzer Reiter, Hunter and Falconer.