When we've had an early breakfast, we feel we miss too much. The early hour or two is so good for park touring, so if your'e watching the clock to make it to the park before opening, or if you miss park opening, you're losing out on prime ride-riding opportunities.
So we grab a little something...fruit or granola bar, that sort of thing...ride some rides at park opening (or try to), then have breakfast (whether it's a character b'fast or something else) towards the end of b'fast time.
But that doesn't work for everyone. We're pretty flexible in when we have "meals" at home, so it's not hard to do that on vacation. For people with more scheduled stomachs that might not work.