I love how people use different ways to express laughter online. You can tell more about the person like if someone says "jajaja"; I know they are Spanish speaking. If they say "wwwww"; I know they are Japanese(or at least it tells me they're into Japanese culture I guess). I don't know it's just a cool thing that is interesting to me.
Anyway, I usually just use "hah" or "haha". "lol" seems to have become almost a sarcastic, condescending way of saying "that's not funny and you are stupid" sort of thing. I never use it seriously.