Depends! I insert lol casually into my text to make it sound less-harsh, and I guess I tend to use haha with someone I'm not super close to. Or if I just want to keep whatever I'm typing free of typos and chatspeak.
I usually say lmao instead of lol I don't know why but with my friends I usually say haha because I sometimes hate using short phrases like idk, lol, omg, etc. and I like to spell it out instead, I don't know why I do, I just do. Unless I am in a rush to type then I use a lot of the shorter phrases.
I feel like it definitely varies. When texting my friends IRL, or at least one friend in particular, it seems to be "Haha", but online it's all "Lol" for the most part. Kinda both? I never really though about it...
I used to be strictly lol. But I met a friend in college who exclusively used haha. Now I mix them. About 75% lol, and the rest are hahas when I feel like I'm using lol too much.