If there are only two to choose which of the BTC or IOTA I would choose BTC. Bitcoin is the king of cryptocurrency and has solid supporters and community already in the market. It is by far the most reliable for me to invest because without bitcoin, the market could go weak for now. I have nothing to say against IOTA because I have not tried it before or even its development. But if you are sure you can have solid belief that it will make you good return in the future then you have the option to invest in both coins with your $10k investment.