Is it better to reply to toxic people in the same manner as them (to teach them a lesson), OR just not reply to what they're saying?

You can't change them, so in the end, saying nothing or being snotty back to them accomplishes the same thing - nothing. I will often leave the toxic people alone and spend effort on the nice ones. Sometimes though, it's just fun to out-toxic their comments and see who else piles on. Just for fun, since there's zero chance you can get them to think "gee, I've been an a-hole. I'll apologize and be nice".

In general? Just move on. It's not worth it.