You can do either, Laura - but be prepared not to get much in the way of comments if you repost them on the mbs as most readers will have already read them, of course.
That said, there will always be new members to the mbs who may not have caught up with them on the Archive and who might take the chance to read them here.
If it was me, I'd simply submit the revised versions to the Archive. That's what most authors seem to do in this situation.
LabRat