Complaint against supervisors
First - a meta comment. Getting out of abusive relationships with one's advisors can be really difficult, especially if said advisor is a big name researcher. That said, once the first signs are in, it is often better to cut your losses and get out of this relationship than to stay on in a bad situation. 

I think that if you have some real complaint then you should make your case to the department administration (head, dean for graduate studies etc). If your university has student support resources (e.g. a student union, an ombudsman), get them involved as well. What happens next is very dependent on the advisor's status within the department, and on your department's administration. 

If yours is not the first case, then your complaint can have serious repercussions towards your advisor. Informing fellow students about this person's behavior is also a viable strategy, as it may protect them from a potentially terrible experience.

The weight given to your complaint is highly dependent on what it is that you're actually complaining about. If your advisors gave you bad advice but otherwise kept their advisory roles (e.g. regularly met with you, provided you with necessary resources etc.) then this could be chalked up to style/bad luck. A lot of administrative matters are beyond your advisors' control, so maybe what you perceive as a failure on their part really has nothing to do with them. If you have written proof of malicious intent or gross incompetence, then you may have a case.

Since you have already graduating, I see no benefit to you in complaining, at least under a very narrow definition of benefit. There is some satisfaction in knowing that you made the world a better place by acting against an abusive/incompetent advisor, again, under the premise that your complaint has real merit.