The best method is if you can work it out together – that does not cost anyone other than your time. Mediation and Lawyers are ultimately if you can’t resolve it or one party is not prepared to come to the table. Sometimes the extreme measure of not paying your rent can cause the landlord to come to the table – what do you know about your landlord – do they have multiple properties – and could you talk to other tenants to see if they have the same issues as you do. What we know from others is (1) good tenants and good landlords sit down and sort it out openly and come to terms (2) when you have one of the sides not playing ball, the question is ‘how to get the other to play ball’ – that could be getting a mediator or a lawyer or even being extreme and holding payment.
I know in our situation for one of the people I work with – we could not get the landlord to terms, so we just sent them a note saying we think 50% is fair and we are going to pay you that.
Final thing – make sure you know the terms of your lease and have read them. In case there are some fishooks in there.