Answer
I assume this is an opinion question, no right answer, so I wrote a short paragraph for each opinion. If this is an essay, you can pick your opinion and broaden what I said, then use the other opinion for your contradictory paragraph.
If you need a thesis:
True: Although words are the best form of expression speakers should plan what to put on their PowerPoint slides before planning what they want to say because it is the backbone of any presentation, and it can help you or others who are lost.
False: Although PowerPoints can help if you need backup, speakers should not plan their PowerPoint slides before planning what they want to say because knowing what you are saying looks professional and has a greater effect overall.
Explanation
If true:
Speakers should plan what to put on their PowerPoint slides before planning what they want to say. Your powerpoint slide is pretty much the backbone of your presentation. If someone can't understand what you're saying, they will just look at your powerpoint. It also helps back up your point and can even help you if you get lost. Let's say you get to your presentation and you just completely blank on what you wanted to say, if you're presentation is also saying what you had wanted to say, you can easily turn around, take a quick look at your power point, and still get your point across.
If false:
Speakers shouldn't plan what to put on their PowerPoint slides before planning what they want to say. Nothing can be better presented than your words. If you are stuttering your words or forgetting what you wanted to say, overall, it makes your presentation for one look less professional, and for two, it can make you seem like you didn't really try, because you have no idea what you're talking about. It doesn't matter if your powerpoint has all of the facts. If you can't convey those facts with your own voice, your presentation has already lost most of its effect.