I have been working with Php/MySql/WordPress for a while now, may be like a year. I am an student, so I don't have alot of time, but I have enough free time to do a job too. Do you guys think I should join a company which offers me some money for what I do for them, or should I keep on working on my own as freelancer?
You're in school so you can afford to dream bigger and thrive to solve bigger problems. Learn to be a great person, not a mediocre developer. Learn how to think and everything else will follow.
If you want to run your own startup some day, then you should start today. Find a problem that interests you now and look for ways to solve it in your own way. Domain names are cheap, hosting is also cheap, work on a project for yourself.
Also, try to refine your development process, php is fine, but you must combine it with patterns such as MVC. Build a cheap computer and create your own development server. Learn Python/Django or Ruby/RoR and more (NodeJS etc.). Host your own version control system (Git, Hg etc.).
Young one, you need to learn to be a hardcore dreamer and level up like mad.
I've been doing web for 10 years and every time I look back, I always think that I learned more this year than many years before combined. Every project I worked on, I always think that I've learned more from it than many before combined. I am 28 now, but I am forever searching and learning.
Good luck and always, stay a hard core learner!
People generally choose freelance work over employment because it means (1) more freedom, empowerment and power over their work and life (2) more money. If you get a job that offers you equal or acceptable levels of (1) and (2), go for the job. If you get the same amount of money, you need to decide how importance (1) is for you. If you by any chance happen to get the amount of (1) but less money, you need to think about how passionate you are about your work and how less money will affect your daily life.
Now, maybe you're really ambitious and still want some of the benefits of employment. If that's the case, get the job but make it clear that you will continue to do freelance work on the side, maybe during nights and weekends. The nice thing about this is that you keep building your portfolio, incredibly important for freelancers, and can pick projects and technology stacks that interests you.