のは, のを
 

Hi, I would like to know which particle (のは, のを) is suitable if I want to sa y "Stop crying!"?

泣くのはやめろ

泣くのをやめろ

Both are "correct" as far as grammar but the native speaker's choice would definitely be the former.

I cannot imagine a native speaker using のを in a command very often. It's far more often used in the past tense as in　マックスフルは泣くのをやめた.