It depends on whether your collar has a lip covering the top of the seat tube. If so, you have no choice but to put the shim on first.
Likewise if the shim has a lip which extends beyond the OD of the seat tube which would then need to be above the collar. (lips on shims that large are rare, but it's something to check)
If the presence of a lip on the shim or the collar doesn't dictate which way it needs to be, feel free to please yourself.
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