well,prob u can get better advices,but since no1 answer to u, i'll try
Atm LC got many changes- some for better,others- for worse.
To play as a witch was always enjoyable,cuz the plents of debuffs . Atm some of debuffs doesn't work on bosses,and without any good attack skill,the witch can use only the reg hits ( they got nice rate of crit hits ) Along with tht ,being a mage,u will get a low defence,and slow speed -movement and attack.U will get a stone/sleep skills- these work on normal mobs,so can save ur life. I cant say anything more about withches,cuz im a wizard,and never got one;P If im wrong for something,let the pro corect me
About wizard - to playing as wizard its really fun in tomb. Only the NS can beat u there
Its easy and faster to grinding there and i would say also a bit cheaper. But after tomb -lvling getting really hard. U will need defence and hp boosts, cuz mobs hitting really hard. If u can aford u a nice +ed wep,then ur low defence wont be a so big problem. The key for lvling in mondshine is to do ur dailies quests in pt.
The bad side of being a wizard is :
- the skills ur 122 skill wil has 3mins cooldown,and 5 mins for ur 132 one.Thats make them a lil useless,atleast 155 lvl,when u get more cast up.Nova is a nice aoe skill with decent dmg,but its not the best skill with red mobs,cuz has a attack buff for the oponent/mobs.
- no stun/stone/sleep skills, u will got only fear ,and with 30% cast only,u cant perm spam it.U wont be able to run away from mobs cuz ur slow speed- even with speedies,some mobs r faster than u ;D
- ur attack speed - will be 14(with self buff- 12).
The good point - if u can manage to hold mobs on u,without dying- u can lvling fast, because of aoes.
Which class u will gona play depends all of ur style of playing,and what u can afford. There r some p2 tht will be prety usefull for u,playing as mage. With the new afinity system,u will be able to use stone/stun/sleep scroll - so no needs to being a witch to use these skills. U can use cast pots too - so the cooldown on ur skills wont be so important. Here u can check for the wizard and witch skills - http://lastchaosinfo.wetpaint.com/page/Mage+skills
its showed required sp,lvl and some information about them . Its a lil out of date,but the new added lvls r for 160+
Gl and hf with ur mage,no matter which one u will choose