What's better, Archer or Thief and why. And please give tips for the one..

There is a really hard thing to decide right there. Let me show you the Pros and Cons of the Archer and Theif:

Archer Pros:

Underused
Long Ranged.
Able to hunt High monsters at early level due to High Accuracy.
Arrows easier to acquire.
Money is saved.

Archer Cons:

KS'ed(Kill-Stolen) a bit at the start.
Runs out of Arrows at early levels.
X-Bowmen(Crossbow Man) is horrid.

Theif Pros:

Overused.
High Attack(LUK) with Stars and Claws.
Can dominate monsters after making 2nd Job Advancement.

Theif Cons:

Really hard start(unless you can get enough money to do Exchange Quest in Orbis).
KS'ed by Warriors without the use of Claws.

I easily took the Archer. This is me, however. Take a think between the 2 of them and decide, I like the Archer because during the 2nd and 3rd Job Advancement, they can hit multiple enemies, since at higher levels, you get a lot of mobs to deal with.

I would go with the Archer because in the 2nd job you won't need arrows with the kill soul bow.

Well it depends a lot.Thieves can jump and attack with stars and can attack with close fighting attacks.archers can't jump and attack but are more accurate.also archers are super bad at close up fighting.So I would pick thief even though at the beggining there very hard to handle

Arcers are better beacause they shoot more damage than theives Archers damage lvl 10-29 900 thieves 600 30-70 3000 damage thieves 2000 and 71-120 is 7000 thieves 6000 so archers are better than thives pick a archer!