Vagrant
Well, this is the aboslute beggining class, you level up 1-15 then it is off to change classes. During this level you get some really basic combos, they are pretty good, but you won't use them much after you job change.
Mercenary
It's the generic melee class, not that that should turn you off, because this class is actually pretty fun. Although you only hack and slash through all your enemies, you get a whole list of skill combos that are really good. If you are using a knight build to level, make sure to stick to using Splmash, Keenwheel, try to get Sneaker, and either get Sword or Axe Mastery, or be like me and get both. As for leveling using a blade build (most do this beacuse it is easy leveling) just use swords, you won't really ever touch your skills after level 40 or so.
Assist
A very fun class to say the least. There are t2o very different class options to go into. There is the Full Support (FS) or there battle assist (which breaks into two subclasses: AOE (area of effect) or DEX). FS' start out leveling slow, no one really needs one at low levels, but once you get to 35-40+ you can hang around high level monsters and get some pretty fast levels. Battle assists are like Merc's but just with buffs and little weapon skills. They are the only first class to get AOE.
Magician
The caster class, not much to say.They seem like fast levelers, and do a lot of damage at low levels. You can go Elementer or Psykeeper, Ele's have huge damage, but little defence, and Psy's have pretty good damage and a lot of defence depending on your build. Some Psy's at level 70 can take on level 100 monsters.
Acrobat
There are two different options, Yo-Yo or Bow. both of which are good at PvP, just Yo-Yo is difficult to level and doesn't get any aoe skills even at 2nd class. Yo-Yo's are a lot better at pvp though, yet Psy's are the best.
Knight
The tank. With a FS i can tank large amounts of monsters for AOEing. Gets AOE at level 65, and in my opinion has the coolest armor (I'm sure most of you would disagree with me).
Blade
Godly at PvM/PvE (whatever you prefer to call it) which is grinding. They can kill mobs in seconds, and they have some pretty cool armor also. Yet they can not kill anything in PvP, due to their lack of defence.
Ringmaster
Best to max your buffs and healing as soon as possible though, yet someone will party you regardless if they're maxed. Leveling is fast, especially since people 10+ levels will invite you into parties. Just be weary, with great power comes great responsibilty, and by that i mean, when you sign on you will most likely be attacked with messages asking for parties. Well most classes receive that anyways, just RM's get more.
Billposter
The fighting alternative. Make money pretty quickly, and you already have aoe, and soon will get another one. Level 80 or so they change to dex and basically become assist just with buffs. Pretty fun if you are making your first character.
Elementer
Godly damage. Just like blade, they are good at grinding, just not too good at PvP. Don't know much about this class, sorry.
Psykeeper
Probably the best class overall. Fast leveling, great PvPing, good skills. The only reason they're so good is because of their skills, it allows them to go full stamina and tank high levels monsters, not that theyll need to though.
Ranger
2nd class bow. I haven't seen many of these, but they look strong, and are pretty good at PvP and grinding.
Jester
The Yo-Yo alternative, the only class that gets no AOE at all. Yes that's right, no AOE, so leveling gets frustrating. I hardly see any of these at all, and I've only seen about 3 or so in my whole FlyFF career. So, if you like being a less popular class, this is for you.