Tough call, probably Ireland (by a hair), but Ross is responsible for a huge number of blunders himself. So it really depends what "problem" it is your speaking of.
Ross: celebrity-obsessed, misguided, questionable intentions, preoccupied with the wrong things (ie: not winning, but rather, filling seats via stadium renevations, water parks, celebrities and other inane non-football related methods), keeping Ireland for some unknown reason, willing to overpay free agents based on name value.
Ireland: ass kisser/yes man to Ross, makes bad impressions on players, after 4 seasons has failed to establish a winning culture in Miami, bad talent assessments ie: multiple mediocre/poor drafts, inability to secure crucial free agent acquisitions, questionable personnel decisions (Marshall and Bell).