Most MMOs give you a starter weapon based on which class you have chosen and then let you have at it for a few levels. Aion is no different and actually goes through these motions twice, since you become a new class at level 10. Each starter class is given two classes that they can turn into. One of the options will allow the player to continue playing much as they have, a Scout turning into an Assassin for example. While choosing the second option will bring about a new play style.
When you hit level 10, you complete a quest which offers you three different weapons as rewards. Confusingly, the offered weapons are based on your starter class and not the class that you have become. It is important to know what weapon is right for your new class because the game does not do a very good job of explaining it. It is very easy to choose a weapon you do not want to use, or perhaps cannot use. It is not the end of the world if you choose the wrong weapon, but it can make the next few levels more difficult than they should be.
Warriors come standard equipped with a sword at level one, and then as they level they gain access to a shield. If you do not have the good luck of a shield dropping for you, then you should buy one from the armor vendor in your main starter city. Having a shield for its defensive bonuses and its special abilities makes moving through the early levels that much easier. Not utilizing the shield's abilities will force you to stop to heal every mob or two, while using it will let you keep going and going. Warriors at level 10 can choose to become either Templars or Gladiators.
Templars continue to play much like the Warrior did. They are the sword and shield class of the game. Out of the three weapons to choose from, Templars should choose either the sword or the great sword. Whatever you do, a Templar should never choose the polearm. It is red for a reason. You may be incredibly tempted to choose the polearm, but Templars cannot use them so it would be a waste. The sword is the weapon type that you have been using up until now as a Warrior, and while it serves its purpose and allows you to equip a shield, there is not any tanking going on at this level. The great sword provides higher damage output, which means less time spent in combat before a kill. Using the absorption shield ability learned while you were still a Warrior, as well as the shorter cool down offensive abilities, it is the best weapon for killing mobs. The great sword is a little better, but it really just comes down to your preferred play style.
Gladiators, on the other hand, do not have a choice to make. While a Gladiator can equip all three weapons offered for reward, the only one they should take is the polearm. The polearm provides the highest damage output of the three weapons as well as a much higher critical strike chance. Gladiators are all about large damage output, and if they do need to tank something, they can always put their sword and shield back on.
Scouts start off the game with just a single dagger. They can also equip swords and later on and learn how to dual wield. While getting large critical hits with the dagger is nice, at these low levels the Scout is the most fragile of all of the classes and a missed critical can mean death. A solution to this is to use a sword instead of a dagger. It provides steady damage instead of spike damage so there is no need to worry about killing your target. As you get higher in levels you can switch back to a dagger to gain the potential to kill monsters much faster. Scouts can become either Assassins or Rangers.
Assassins continue to work the same way the Scout does, using stealth and high damage to gain kills. There are no new weapon options really for the Assassin, you can choose to pick up a dagger or a sword that is of higher quality than the one you are using and continue on your way.
The Ranger is probably the largest shift from starter class to second class in the game. The play style shifts completely, from attacking monsters head on to kiting them and firing from range with a bow. Rangers should take the bow option from the quest reward, without one they cannot use their new abilities. Rangers also need arrows, and vendors do sell them though it can be hard to locate the appropriate one. The best place to find arrows is after you leave your race's capitol city and go to the next quest hub. One of the vendors there will have them and there is a lot less guessing to be done.
Mages get spellbooks. Yeah, it is not that exciting. A spellbook gives the Mage the ability to damage targets from range with magic while not consuming mana. Perfect for when you have a weakened target and you do not want to burn an entire spell when all it needs is a few love taps. Most of the damage done by a Mage will of course be through spells, so the spellbook is mainly used for its stat bonuses. Mages can choose between turning into a Sorcerer or a Spiritmaster.
Sorcerers continue to play just like Mages have. They gain new spells at level 10, but otherwise continue functioning in the same way. As always, there are three weapon options. Two spellbooks and this new weapon called an orb. One of the spellbooks gives a higher damage bonus, while the other gives a higher accuracy. The difference between the two spellbooks at this level of play is rather minimal and they work just like the spellbook you already have. The orb on the other hand is actually a melee weapon in disguise. It deals the highest amount of damage out of the three weapons by a good amount and is best suited for the Sorcerer. There is nothing wrong with choosing a spellbook, but Sorcerers do not have many situations where they will be casting a spellbook at something instead of casting a spell.
Spiritmasters can choose the orb if they want, but it kind of defeats the purpose of having a pet tank for you if you are just going to run up to the monster anyway. Spiritmasters can continue to blow through their mana at a rapid pace much like the Sorcerer, but they do not gain the same amount of regeneration as the Sorcerer and the best way to utilize the pets is to actually use them. Using a spellbook as a weapon will allow the Spiritmaster to deal low damage from afar without wasting any mana or drawing aggro.
Priests wield maces and use a combination of spell casting and melee combat to get through the levels. While dealing less damage than the other three starter classes, a priest is the most solid and should never find themselves in a situation where they end up dying. They are the only class with the ability to heal with spells. You can use spells exclusively while questing, but the maces provide additional real damage, and are not just for show. Using spells to cast at a mob until it gets close, then using the mace's abilities, then switching back to spell casting until the melee abilities are off cool down is the typical way to go about killing things. Priests can become Clerics and Chanters.
Clerics focus on their spells and healing and learn how to use shields. Out of the two options they are the most similar to the Priest. The three weapon options are very similar to the options a Mage gets; two different maces and a staff. Clerics work best with maces because it allows them to wield shields and since they focus on their spell casting they do not need an offensive melee weapon, just a defensive one.
Chanters continue to gain new spells but take a shift from casting most of their damage to gaining more instant damage spells and melee abilities. At this level they should take the staff as it deals more damage and works well with their weapon imbuing abilities, letting them get the most out of their new magic. At higher levels they may want to switch back to a mace and shield, providing higher survivability at the cost of less damage output.
As long as you do not choose a weapon which you cannot use, then you should be okay. Even if you do, vendors sell lesser versions of all of these weapons, or you can keep using your weapon from before you hit level 10. It can feel lame to choose the wrong weapon, I know I did during beta on my Spiritmaster, but it is a lot better than choosing the wrong class and redoing all 10 levels. The next weapon upgrade is achieved around level 13 or 14, so it is not a huge amount of time to get something new. But it will be harder to do those levels if you have chosen the wrong weapon. Especially if you are a melee class because the line between being able to move through monsters and having to rest between each kill is really close.