-To describe extended past states we can only use used to
There used to be a church here.
I used to have an old car.
-To talk about regular and important habitual behaviour.
I used to smoke.
Maria used to go to ballet lessons
Would is generally used when the time or topic are clear, otherwise the meaning of this modal verb wouldn't be clear.
(one customer to another customer in a shop)
I used to buy that, but it's a waste of money.