Which demand of Mahatma Gandhi was most stirring?

The most stirring demand of Mahatma Gandhi can be the demand for the abolition of the salt tax. The salt-tax was introduced by the British to protect their monopoly 

As far as Mahatma Gandhi was concerned the salt-tax was the biggest symbol of British oppression as salt was an everyday item of India’s poor. Abolition of the salt tax would go a long way in improving their condition.

For further reading check the following articles:

• Salt Satyagraha
• India’s struggle for independence