I'm with Puppi. It depends on what I'm writing. In texts, emails, or messaging with friends, I write any variation of lol, LOL, LMAO, etc. If I'm writing a story, I describe the laughter. I will very rarely write "ha ha ha" or something like that, unless the character actually said it.
"Ha. Ha. You're so funny." I rolled my eyes.
I erupted in laughter. The joke wasn't that funny, but the look on his face was priceless.
John's body shook with silent laughter.
He covered his mouth with his hand, trying to suppress a giggle.
If I am writing texts or emails that a character sent, then I will use text speak or the appropriate informal language.