Best words in Chinese characterizing "cynical"?
犬儒
KEY defines it as:

cynic (esp. as Greek philosophical school)

and 汉语大词典 defines it as:

原指古 希腊 犬儒学派的哲学家。他们提出绝对的个人精神自由, 轻视一切社会虚套、习俗和文化规范, 过着禁欲的简陋生活, 被当时人讥为穷犬, 故称。后亦泛指具有这些特点的人。

Here’s an example of usage by 鲁迅 from Miscellaneous Thoughts

《小杂感》
蜜蜂的刺, 一用即丧失了它自己的生命；犬儒的刺, 一用则苟延了他自己的生命。

Which translates to something roughly like:
The sting of a bee, once used terminates his life; the sting of a cynic, on the other hand, is able to prolong his existence.
Eileen J. Cheng's translation:

Once a bee uses its sting, it loses its life immediately. Once a cynic uses his sting, he drags out his life momentarily.

If it is good enough for Mr. Lu Xun then it should be good enough for anyone.