It'll depend on how much you want to brace it to stop vibrations.

0.6/0.8mm would need a reasonable amount of bracing (or strategic folds/ribs/kinks) to give it strength on large flat areas and avoid it resonating.
1mm shouldn't need much reinforcing except for large flat panels and around openings.
1.2mm shouldn't need any reinforcing.

Off course, the thicker you use, the more effort it takes to cut/bend, and weight can quickly add up, so it's a bit of a trade off.
Ideally I'd probably use 0.8 for large simple panels with a few ribs to save weight, then 1/1.2 for any with openings/doors with suitable folds to provide a strong structure. In practice, I'd likely use whatever I have lying around at the time.