At character dinners, you're greeted by and take pictures with Donald, and roaming characters are Stitch, Chip & Dale, and/or Goofy.
At character breakfasts, you're greeted by and take pictures with Mickey, with Minnie and Pluto roaming around the tables for pictures.
Breakfast is with Auntie who plays the ukulele and sings, character dinners are with Uncle who tells stories about the Menehune.
If meeting specific characters is more important than the food offerings or price, choosing breakfast vs. dinner matters.
To the OP, I'm an early riser although I've never booked the first reservation at Makahiki. From what I've seen walking the path between the lazy river and Makahiki's outdoor dining area in the morning, the characters do seem to get an early start. Mickey is almost always out early when the restaurant opens up.
To add, while sitting outside by the koi pond is very nice and my preference as well, note that Auntie's "show" takes place mostly inside. Auntie does have bits where she invites the kids around and they get to perform and play with props, and follow her in a line around the restaurant. This is the same with Uncle at character dinners.