I think it depends on the make-up of your family.
As recently touring with young (infant/toddler/preschooler) I like the flexibility offered by getting your 3 Fast Passes scheduled and completed by lunch time (12-1 pm) as that is when the kids are definitely ready to roll. Going with preschoolers means you aren't probably going on a lot of the normally long "thrill" rides anyway, and ANY line skipped is a bonus with kids that may be done by mid-afternoon anyway. Who knows if they will be napping or need a break when you have an afternoon or evening Fast Pass scheduled.
Unfortunately this does mean a "wasted" Fast Pass in the morning usually. I've had a 9:30 AM Disney Junior and a 9:30 AM Enchanted Tales. Both had zero line that early, I may have been better off scheduling a mid-afternoon fast pass somewhere else, BUT because of that we had flexibility at lunch to do other things and other "must do" rides (for us) later. It worked out because my son ended up napping like 90 minutes in the middle of the afternoon, so not like we could have done any rides then anyway (at least with him).
I also then like the flexibility of looking at
MDE and deciding what to do next, based simply on what FP's are available for your 4th, 5th, 6th, etc. I've been surprised what I've been able to schedule same day and only a few minutes from the current time (Rock-n-Roller coaster for example).
I also choose my fast passes based on location to minimize backtracking. (key with young kids).
For example . .my last fast passes at MK were:
Buzz, then SDMT, then Peter Pan. That gave us the morning in Tomorrowland and put us in Fantasy Land by lunch. In between fast passes you can do other things in the area, Carousel, Teacups, Philharmagic, Small World, Pooh, Princesses, whatever.