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It varies from person to person. o: What kind of things are you looking for in a character?

<3 thieves.... but then, I'm biased. I love agi characters.

They typically can give damage that can challenge swordie base characters, and by the later levels, most assassins and rogues I've leveled with on my priest outdamage the knights and crusaders, unless they're either really well built or the sader's a grand-cross build--although I did level with one sin once in niff2 that actually managed to pull exp/hour that was equivalent to what I would get leveling there w/ a gc sader or in some place like magma or ct hos with a wizard. Of course, there's always the chance that I just happened to get partied w/ some really bad knights and saders.

Thiefs are easy to start off with because they have high flee and wont get hit so much, but if they do get hit, its over. While a swordy is a good all around char that can do pretty much anything in the game. surprised

You kinda have to take in the pros and cons for each class. Also you factor in your playing style, and all the possible builds (I prefer Speed Hybrids personally).

Swordsman - Good all around character. High HP gain. Low Sp. Decent power if sword, high power if spear. Pretty fast if using swords (Knight), quick also with spears (Crusader). Flee isn't that high but just enough to dodge non-MVP monsters. Armor class is top-notch, and couple with high HP, they have pretty long staying power (Crusaders with Reflect Shield and Defender backed up by a full support priest). One con is that they are quite hard to level at low levels, and sp isn't enough to support skill spamming.

Thief - Incredibly quick character with high flee rates (good for all around PVM). Sneaky and cunning. Daggers and Katars are fast and quick killers (especially Rogues at high levels). More chance of earning items/money with Rogue w/ Mug. HP is sorta lacking, and with no armor to back them up, a well placed Vulcan Arrow, a few Double Strafes, a timed Frost Diver + Jupiter Thunder, or a connected Asura Strike could easily take them out. Anything that can hit a Thief class is considered a death threat.

i love merchant classes because i'm a masochist and enjoy suffering the pain of leveling slow merchants!

I think that theifs are because they have a better weapon choice to my perspective & they are faster generally. <3 Double Attack.

Thieves.
Main Reason: Assassins are one of the best classes in RO. I have played Assassin Cross, Stalker, Lord Knight, and Paladin. I will go through Assassins, Rogues, Knights, and Crusaders.
ASSASSIN- Major poison, high damage when you get katars, or you can go two hand dagger/sword. Enchant Poison, Katar Mastery, Stealth, and Sonic Blow are a must.
ROGUE- I forget the name of the skill that allows you to move while hiding, but it helps a lot for stalkers. You have auto-steal, and you can now steal Zeny from monsters. A class that you should do if you need a lot of money.
KNIGHT- The only skill I'd recommend would be 2-Hand Quicken. You can also ride a Peco (extra movement speed) You also get a lot of HP, but if you're fighting a strong Assassin, you're dead meat.
CRUSADER- A good VIT class, with a certain skill at level 10 you can get +2000 HP. Spear Quicken is a must, along with your PecoPeco. You can get a skill called Grand Cross, and it is also a must. You would be better off fighting undead monsters with Crusaders, so take my advice if you decide to do Crusader and fight the Undead.