I would like to create an arcane caster. Which class should I pick?

So you want to be a caster?

In DDO, there are two classes that are considered mainly arcane casters. Those are the Sorcerer and the Wizard. But, along with those classes there are several that are partially arcane casters. Those are Bard, Artificer, and Ranger. I'll go through all of them.

Main Casters
Whether it be buffs of offensive spells, these characters usually don't do much besides spell casting. It is not recommended to wear armor as that can lead to arcane spell failure. Spells for both are here

Wizard
Wizards tend to have higher spell DCs. This helps the spells they cast actually land on the enemy. Their main casting stat is intelligence. The also have bonus feats at levels 1, 5, 10, 15, and 20. Most are metamagic feats, which allow you to make spells more powerful but at the cost of more spell points. It is also worth considering that Wizards have slightly less spell points, but they can change spells as long as they are rested and in a tavern or near a rest shrine and have the spell in their spell book.

Currently there are two enhancement lines available for the Wizard. The first and more commonly chosen is the Pale Master. It involves casting necromancy spells that are quite powerful. You can also put yourself in a form that makes you more powerful, but you are unaffected by regular healing and repair sells and must be healed by negative energy.

The second available line is the Archmage line. It gives you more spell points, but also allows you to spend some of your spell point limit to get spell like abilities, which are basically spells that only cost one spell point. This makes it easier to cast commonly used spells.

Sorcerer
Sorcerers big boon is their spell point pool. They get many more spell points and can also get more spell points from items then Wizards can. The big drawback for most is that you can only swap your spells with hefty costs(Blood of Dragons). The Sorcerers main casting stat is charisma. Sorcerers enhancement lines are known as savants and they are one of the reasons people go sorcerer.

Savants are essentially elemental masters. There are four types, each corresponding to an element. They are Air Savants, Water Savants, Earth Savants, and Fire Savants. They become much more powerful in their element, but at the same time become less powerful with opposing elements. I.e. if you are a Fire Savant, you lose power with you air and water savant. They also gain spell like abilities related to their element.

Partial Casters
These classes are part caster, but also part something else.

Artificer
Along with using crossbows, Rune Arms, and a companion, Artificers can make some lethal casters. They can not only do some great offensive spells, such as Blade Barrier, but they also have some great buffing spells like Elemental Weapons which can improve both yours and a casters party. They use intelligence for casting. If you like doing some great ranged damage with some high damage casting on the side, this may be class for you. Spellbook here.

Ranger
Rangers can either use bows or dual wiled some sort of one handed weapons. But I'm not here to talk about that. Rangers have some pretty useful spells up their sleeves. Rangers use wisdom for their casting stat. Rangers spells are mainly buffs and healing, with not that much worth in offensive spells. If you want to dual wield and/or use a bow and still have some self healing and buffs, this is probably the class for you. Spells can be found here

Bard
Bards are the best buffers in games. They cast with charisma. Their songs from Warchanter, Spellsinger, and Virtuoso, along with their songs that come with their class they can be great. A lot of their spells are buff and heal spells, but they also have lots of spells that can charm and basically get less damage on the party and more on the enemies. Spells here

Conclusion
Whether you want to be a full on caster or a partial caster, it's up to you. Just remember to pick what suits your playstyle.