it really depends on the situation, if you are face to face with a warrior you may get destroyed they can charge you and take your bow out of the equasion, all you can do at this point is run and find some friends to take care of him. and an assassin if they stealth up to you or use disquise skill they can be attacking you before you know what is going on, which many times results in death they have too many stopping skills to run away.
now if you catch one of these unaware you can get a few good skills in there before they locate you. then if they find you they have to attack, the assassin is at a huge disadvantage here especally if you have some dex to raise your attack or use a skill to weaken them. The warrior can ignore your arrows only 6 seconds at lvl 1 but that is like 2 arrows, so he could get upto you and recover.
though if you are in a team with a healer and guardian or warrior against a warrior, priest and mage while the warriors are fighting you can pick off the priest and mage, while the warrior quickly dies