'Used to' is much more common; 'would' is quite literary, or just knowing/self-aware. I think the difference is more one of register than of meaning. I would say 'In the sixties I used to go to school'; I might write something like 'During my schooldays I would often walk to the station and save my bus-money.' In both cases I'm dealing with something I did regularly in the past. - but the tone is different.
Both 'used to' and 'would' can be used for past habitual actions, happening, and events, but only 'used to' is used for past states. Past states are those described by verbs of being, seeming, possessing and those describing feelings.
As BobK implied, it's usually safer to use 'used to'.