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Permission to use, copy, modify, and/or distribute this software for any purpose with or without fee is hereby granted, provided that the above copyright notice and this permission notice appear in all copies.
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MIT also explicitly allows sublicensing, whereas ISC does not.
While (to the best of my knowledge) ISC does not disallow it (so long as the original license is around somewhere), sublicensing is scary to a majority of non-lawyer developers.
So if one wants the possibility for sublicensing to be open, MIT should be preferable (for the sake of clarity to the general user). If not, ISC is simpler and (due to the above) at the very least discourages such behaviour.