I would prefer 12t.
I want to be able to press in a few different bearings and see how they stand up to use / pressure washing etc, and 688 is a nice common size with options from the very expensive (e.g., enduro xd-15) down to the very cheap. So far, I have learned that ZTTO seems to use the 689 size.
I messaged a few aliexpress sellers i found using the the search terms you suggested. Thanks!