We have a chart showing the days on which each park has EMHs for the first half of 2006. EMHs are distributed widely enough that there are few certainties, however, outside of the MK on Sunday evenings and Thursday mornings. Here's a summary:
Sunday: MK almost always has evening EMHs. Epcot has the most mornings (13).
Monday: AK and DS tie for most mornings (13 each), and evenings are almost evenly spread out among those parks, too (14 and 13, respectively).
Tuesday: Epcot mornings (19) and MK mornings (12). If any park has evening EMHs, it's probably Epcot (12x).
Wednesday: Most commonly AK mornings (12s), never EP or DS. AK (17) and EP (12) most common evenings.
Thursday: Only park to have EMH mornings is MK. Most common evening is Epcot (11x)
Friday: Most common morning is DS. Most common evenings are Epcot (20) and MK (12).
Saturday: Most common morning is DS (20) and AK (12). No park has Saturday evening EMHs.