Hot technology? PHP has more jobs than Ruby and Python put together. Theres still a lot of legacy code. You teach a beginner Ruby on Rails he will have less of a chance finding a job than you teach with PHP. Only people using Ruby on Rails is mainly startups and I'm sure they are not looking for people who just started learning Ruby on Rails. PHP gives you a clear overview how you can embed code in an HTML and also use a database with it makes much more sense. I will definitely pay for it if you went this route but I got my fingers crossed good luck.