How good and easy to use certain software is, might depend on the website. So it might be best to use more than one tool if you want to extract data from different websites.
https://www.google.com/search?q=extract+data+from+website seems a good start for your research.
I want to know which web data extraction software is the best. I want a tool that can extract the data showed after you click a button on the web page or any data that not showed in the screen but can be found in the HTML source... If the tool is free, it would be better..
Any help would be really, really appreciated.