Post-bacc is primarily for non-trad students who have not done most of the science pre-reqs. SMPs are for students who wish to re-mediate their GPAs. However, for DO schools, you have the additional option of retaking courses that you did poorly in. If you were to retake those failed courses and do well in them, you could significantly increase your GPAs. I would strongly suggest retaking courses since it's much cheaper than SMPs or post-bacc and take less time.