I always go to AM EMH (virtually every day of the trip that we did not do a PM EMH late the night before)... never ONCE regretted an AM EMH... they are amazingly empty and easy to ride the open attractions.
If that park THEN starts to fill 2 to 3 hours later... WHO CARE'S?
Were happy with "doing" that park for the day and we can HOP elsewhere or do lunch and take a rest until later.
PM EMH's are a mixed bag. I've been when they were PACKED... but on other nights (sometimes within the same trip), the crowds were basically so low that it was like "free rides" on all the open attractions.
Those who have attended PM EMH's and say that "they are TOO CROWDED" are right... but ONLY for the nights they may have attended.
I can say, from personal experience, that they CAN be EMPTY, or FULL or somewhere IN-BETWEEN for attendance, often within the same week.
It can change so much (either way), that saying it was "like X" on a given night, can be meaningless on another night in the same time-period. So, you simply don't KNOW unless you go.
Its similar to saying that you attended on a given night and it rained, so guests should never go on that night because it will probably be rainy.
And, considering EMH's are FREE to attend... if its busy, just people-watch or hit the exit (where ELSE are ya gonna go at 10pm, anyway?)
But if its not busy... you're ALL SET for EXTRA FUN!