As PP noted, it's really about what our goals are for the day. In MK, we like to start our day in Adventureland, so we go left, head into Frontierland do BTMRR and Splash and then work our way around to Tomorrowland. My DS is 9, however, so we skip attractions like Winnie the Pooh, Dumbo, etc.
In EP, it's really dependent on our FP+ and we typically go to EP more than two days, so we'll either start at TT or Soarin' depending on our FP+, then work our way to the other side then head to WS, usually starting in Mexico.
In HS, we typically go to the left, but we don't do RnRC or ToT (as of yet, DS will probably do it next trip)
In AK, we start in DinoLand USA (to get in as many Primeval Whirl rides as possible!) and then work our way to Africa.
We go frequently, so our order may not be similar to those trying to hit bigger, more popular rides, first.