Splitting Them Up

At some point, every parent of multiples is faced with this question "Do I separate my children in school?" It has been something that weighs on my mind as the beginning of each school year approaches.
When my daughters started preschool last year, they only went two days a week. I talked with the head of the preschool program and she suggested I keep them in the same class the first year. She had some good points: I wouldn't have to deal with multiple field trips, multiple in-class birthday parties, all the homework would be the same. On the first day of school I was so glad I made the decision to keep them together. My daughters had were on the verge of turning three. Many of their classmates were already four. My girls were the teeny, tiniest things in that room. It helped to have them together, simply so they didn't stand out.
When the time came to figure out what to do for this year, I decided to keep them together again. I really like our teacher and I couldn't imagine only having one or two of my daughters in her class.
I'm pretty sure I'll keep them in the same class next year for their final year of preschool. But then comes kindergarten. They'll be in a different school, so initially I thought I should keep them together to help ease the transition. Then I thought maybe it's good to have all the changes come at once. I still have some time to think about it.
Until my daughters are in high school, I doubt there will be a chance to truly separate them... in other words, putting all four of them in different classes. Our school district isn't small, but it's not so big that the elementary schools have four classes for the same grade level. I'm not going to spend my time driving them to and from school all day, so splitting them into am and pm kindergarten won't work. Also, don't even suggest putting them in different schools. Not. Going. To. Happen.
So then what? How do I split them up? Two and two, most likely. But which two? We're giving them a second bedroom in the spring, so I doubt I'll want to put the "roommates" together. They'll get enough of each other at home. There are some personality conflicts on occasion and some of the girls tend to thrive out of the shadow of the others.
Clearly I have a lot to consider over the next year and a half. I'll let you know how I sort it out.