I think they are both great ... it comes down to whether or not you want to get up that early and/or stay out that late. When we were there in late April, the evening hours didn't get over until 2:00 am. I usually go to bed at 10:00 pm, so that was really a stretch for me.
If you can do the evening hours, though, I think you will find that most of the rides are walk-ons after the first hour.
Make sure you know which attractions are open during this time so that you do the non-EMH attractions during the regular park hours.