Like Robo says, if you are a morning person and can get to the park for EMH, go for it. And if you have park hoppers and the flexibility, if the park gets too crowded, you can always hop to a different park. Of course, there's no guarantee that when you hop to another park midday, it won't also be busy. I'm guessing that most parks are going to be busy mid-afternoon. And if you are planning your schedule around ADRs, you might not want to park hop.
When I first started going to Disney World as an adult around 10 years ago, the conventional wisdom was to stay on site because EMH was so awesome. So we completely planned our trips around EMH, and it was great (we typically go slower season: January or September, but have also made trips February and April school vacation weeks). That was back when evening EMH was 3+ hours and AK had evening EMH too.
In the last few years, we started noticing that parks seemed more busy at 8am on an EMH day than at 9am on a normal day. Mainly HS, but sometimes also MK and AK. This made sense combined with the new prevailing wisdom on easywdw.com that you should avoid EMH. So on our most recent trips, we planned our schedule around morning EMH, enjoyed the extra hour of sleep.
Therefore on our last trip at the end of April, we avoided HS Saturday because it had morning EMH. Instead we went to HS on Sunday, easywdw said that was the best park to go to. The park was jam packed. But I'm sure HS was also packed Saturday for EMH.
With information so easily available on the internet, and with the parks so popular year-round, at what point does avoiding EMH become a bad idea? I avoided HS on Saturday because of EMH, should I have also avoided HS on Sunday because easywdw said it was the best park? How many people went to HS Sunday because it was the day after the EMH day? Or was it just busier that Sunday because it was the weekend?