There are always good sides and bad sides to every country and city, and the choice can be difficult. But before going to Japan—or any foreign country, for that matter—it's important to be resolute about your objectives. If you decide to apply for a working holiday visa or enroll in the JET Program, you should have a clear objective in mind. Not just "I wanna go to Japan" or "I wanna teach English in Osaka". Those underlying desires are important, I don't deny that, but you should also create a practical plan for what you're going to do there.
If you decide to just wing it and fly there with a working holiday visa tucked in your passport, you might get lucky and land a job, but in most cases, you'll have to spend time looking for a job. That is why it is important for you to think about the steps that you're going to take after getting off the plane. You can do research beforehand. Use the Internet to look for opportunities. Send resumes beforehand (but tell the employer that you've already booked tickets for this particular date). Check GaijinPot. Try FindStudents.net. Et cetera. There's a lot you can do remotely.