Not just on this site but of any board. And not the neverending ones like religion vs atheism. Thinking of the kind that is topical.
I’ve intermittently posted on various debate boards and have read some great posts/threads. But the best (imo) was the Elián González custody debate. Had so many facets, at least where I hung out at the time. We did have a fairly equal liberal vs conservative population but one interesting thing was that you couldn’t always bet on that mandating opinions. Everything from dead set conservatives backing father’s rights to socialists believing he was better off in the US. The debate was so passionate and also led to many involved ancillary debates (legal/legislative/etc). I felt like I actually was learning things.
So, what’s the best debate subject you’ve ever seen. And why?
Edited to add: Runner up was the topic, “should no insurance/charity patients be lower priority to get the luxury birthing suites?” Good, god - that’s a recipe for passion on a motherhood site.
does he wear boxers or briefs?
I think those jersey boxer-briefs. If a guy has a decent ass it’s a nice look.
One favorite I’ve seen recently was “Animal Fight: Who Will Win?” Where basically you put a ton of animals in the coliseum, provide a water supply but otherwise stay out of the fighting, and guess which animal wins. (I’m not sure if it was on this board or another, that’s why I’m explaining it.)
Cake or pie? Alliance or Horde? AMD or Intel? Coke or Pepsi? Paper or plastic? Firefox or any other browser? PC vs Mac? I can’t decide which argument is my favorite, I like all of these.
Not on this board, but the best debate I ever engaged in was over the Terri Schiavo case. Deeply held beliefs on both sides of the fence, but I had the benefit of being right. 
Second best was regarding the “War on Christmas.” Same board, but it was years ago. I know the phrase has been bandied about for awhile, but it was the first year I remember it being prevalent. Sadly, that argument has gotten old and doesn’t hold the same interest it did then.
Which is better: Bread or Pizza?
It is unwise to encourage the spread of Civil War.
Tastes great less filling has never been settled.
The one about teleportation booths, and whether the person that comes out the other end is really you.