Definitely bitcoin. Although, I want to note that my choice is such only now. If, at the time of purchase, my analysis would have shown that by purchasing IOTA I could potentially earn quickly and a lot, then my choice would be made in favor of IOTA.
You must understand that nobody cannot say something for sure on the crypto market. Having made a certain choice, after 6 hours you can greatly regret it. So you always need to be careful and be well versed with what to buy and sell.