Ok, the stuff gets real now:

Whether you agree with them or not.

Several hours conversation ...

The stimulating conversationalist expresses an opinion honestly

without the use of pejorative language -

preferably giving reasons for the opinion

based in personal experience   professional research or sound logic.

It is more stimulating if it's possible to offer an original angle or something new

or if the response is creative.

Humour is good if it is not disrespectful.

Trolls get pleasure from provoking and hurting others -

rather than stimulating they first dangle bait and then torture the caught fish.

I never answer the questions or responses of trolls

unless occasionally by accident if they are new and I don't yet know them.

Once is more than enough.

A stimulating conversationalist is someone from whom I can learn.
Doesn't matter what it may be: whether it's abolition of the death penalty, or an amazing experience, or how to cook the perfect fried egg.
I must learn from him/her; and, more important, WANT to continue learning more.

lol

Very well said.

If I told you I'd have to kill you.

What kind of conversation do you most enjoy, Mr Vern?