JavaScript
That's it. Not python. Not .NET. Not Ruby on Rails. Not PHP. JavaScript. If you know JavaScript, you can do front end, back end or full stack web development, and there is no "best" in web development. Please get out of the mindset of what's best and whats not, as that's irrelevant in the software development world. You use the tools/ languages that you need to to solve the problem on hand as you are developing solutions, and not websites.
Here is a 100% free coding bootcamp that this guy runs on twitch, and it's starting today in less than 2 hours (6:30pm EST to 9:30pm EST). Sign up and start attending lectures; this will be the best thing you do and you will be a software developer by the end of the 30 weeks of the bootcamp.