Well, it will be a while before Selenium overtakes QTP. QTP is still preferred. Selenium is getting some noise since it is open source and yes it is good . It really does not matter which you choose. once you learn one, you should be able to use others too.  once you learn how to drive a car you are able to drive a Ferrari or a Toyota, can't you :) ?

However, in my humble opinion I think it will be better to learn QTP and Quality Center since lot of organization has it and it might be easier to find a job. Just a thought.