One important factor in determining whether an antidepressant is likely to produce a discontinuation syndrome is its half-life. If an antidepressant takes a longer amount of time to clear out of your system, you are less likely to experience a sudden drop in serotonin or its attendant discontinuation syndrome.
Of all the antidepressants, Prozac (fluoxetine) has the longest half-life (2-3 days). Not only that, its active metabolite, norfluoxetine, has a much longer half-life (from 7 to 10 days).
Because Prozac takes so long to metabolize and be excreted from your body, this gives Prozac a built-in tapering off and reduces the likelihood that you will experience a discontinuation syndrome with it.
Moore, David P. and James W. Jefferson. Handbook of Medical Psychiatry. 2nd ed. Philadelphia: Mosby, 2004.