What type of person are you? The kind that seeks to make others happy, agrees all the time and attempts to validate others, or the type to take the other side of every argument just for fun?
I try not to be overly argumentative, and if voicing my disagreement is just going to lead to a circuitous argument without anyone actually changing their mind, I'll stay quiet. If I am engaged in discussion where there's a desire for something beyond argument for its' own sake, I will try to recall something that isn't just the opposite of whatever's been stated, although this may lead to me having to explain how exactly whatever I said is related.
More confrontational than agreeable, but I do try to keep my focus on the other person's arguments and actions rather than saying stuff about them as a person. I've found that I have fewer regrets, and fewer straight up fights, if I stick to that. And sometimes, rarely but still, they'll actually listen if you make a point of not insulting them for believing something different from you.
I'm still agreeable in my everyday actions because I don't know what the people I'm interacting with are going through. But now I'm much more confrontational in a learning setting. Personally I like debates, assuming both parties are interested, but I usually don't go out of my way to start one.