This is a topic that people get really passionate about. I don’t really understand why, because really, it tends to be personal choice. But here’s my opinion.
I don’t like italics.
I know the author is just telling me how to read something, and it’s fine for them to tell you which words need emphasis, but I always find it jarring. I can decide on my own which words need emphasis, and a lot of the time I would’ve put the emphasis on those words anyway. Plus, I like the voices in my head when I read. I like that my brain does the acting. It doesn’t need any direction on where or where not to place emphasis. I was reading The Heart Shaped Box last night, and there was emphasis on a word that the voice in my head didn’t want to emphasize. So I did what I wanted.
I do use italics in my writing sometimes, but not for emphasis. If there’s a sound effect, I tend to put it into italics. Or, when I’m writing in third person limited omniscience sometimes I put thoughts into italics. In the story Playing Dice with the Cosmos, I have two differing realities, one in the real world and one within a game of Dungeons and Dragons, and everything within the Dungeons and Dragons campaign are in italics. I actually considered putting those sections in a different font, but it always looked so cheesy, so I went with italics.
Whereas I don’t really like italics much, I really dislike parentheses. Parentheses are sometimes referred to as ’round brackets’ but they do have their own name. As memory serves me, and it was twenty years ago, author W.D. Valgardson told me that you can ignore anything within parentheses, and I kind of discovered that it’s true. Anything that you put into parentheses is an aside of sorts, and therefore you don’t really need to read it. (Forgive me for being a name dropper. See, you didn’t have to read this!)
I suggest if you’re writing, and you put something into parentheses, during your editing process you delete it. If it isn’t important enough for its own sentence, it isn’t important enough to remain included in your piece.
I’ve heard parentheses compared to speed bumps. I have to agree.