AM EMH is roughly the same in every park. Less people than normal opening rope drop but not always much less. It's the 10-11am when the first wave of we're not waking up early guests come so you have an extra hour before that happens... (second wave is roughly noon if your trying to plan fastpasses before a afternoon break).
Don't plan around this next point but I've noticed if you happen to be at WDW when there is a 3 or less crowd that 75% of the guests are rope droppers and they pack the place right away and it's the afternoon when they resort break that has nobody around and short waits. I've seen it several times but that low of a crowd happens only on a few days a year you can't plan for it and its impossible to guess which day it's going to be to try to witness it again.
Also if you happen to be around on a 5 year anniversary (oct 1 for mk(2016) and epcot (epcot being 2017), don't remember the others) you'll find rope drop to noon to be a dream crowd as everyone generally gathers for some special speeches and things and then go off to buy that day only merch.