I feel it is better to undergo formal training on web development at an institute. Even if it is a small one, if it has a good reputation of teaching the course, you should join up for admissions to that course. You can always opt for a short-term course of 3 or 6 months or one that is conducted only on weekends. You can find out from students who are currently doing the course there about whether they have benefited. You can just hang around outside before/after class and ask students directly for feedback. That is the best way to get a first-hand review of the course modules and faculty!
The advantage of doing a course from an institute is that you will get a physical certificate on successful completion of the course. This formal certification could well be a plus point in your C.V. when you are seeking a job. On the other hand an interviewer maybe skeptical of your qualification & skills if you simply say you did online self-learning only without formal training.
Self-learning is great to hone what you do know, but a formal course training is far better since you will not only learn to work on projects, but get a proper assessment done to check how well you learned. Online learning alone won't help you to guage your skills at web development.
Finally, it is also possible that the institute provides placement offers or a short internship stint. So go for the training.