They have two different purposes, you just can't decide based on which is easier
HTML is a method to display things over the internet. Mysql is a type of database and PHP is a programming language commonly used with PHP.
HTML will be easier because there is far less to learn about it. Honestly, I wouldn't waste ANY TIME on HTML, just go grab Dreamweaver or something similar and that should be all you need. There, you've got HTML covered, now go learn PHP/MYSQL. You will learn a whole lot more with php and mysql