Hello,
I have actually moved both of my kids. My first was moved to a new K because we moved out of state. We moved her again for 1st grade because we didn't like the private school she was in and we moved to a great public school district.
My second daughter was moved after Pre-K because we sent her to a local private school for Pre-K.
Both adusted just fine in each situation. They love where they are now and have made new friends and really don't remember much of pre-K or K at all! If it makes no difference to you and either situation will be easy for you to get him to and from school then I say whichever school you prefer will be fine.
One thing I can say about when my 1st went to K is that she was TOTALY bored for the first half of the school year. She went from one private school in KY to one here in MI and the whole first half of the year they were learning what she had already learned in pre-K! This was the biggest reason we chose to stop paying so much in tuition and just put her in public school.
So, when you go the parent night make sure you try to find out as much about the curriculum as possible. Maybe corner a teacher and try to compare what your son has already learned to what they will be teaching :o)
Another thing I have noticed from one to the next is that you seem to get more info as a new K parent rather than a new 1st grade and up parent. They tend to focus more on helping out the K parents because most of us are doing this school thing for the first time. That's not to say if you ask they won't answer, but it helps to have the info ahead of time so you actually KNOW what to ask.
Whatever you decision, I wish you and your son much luck!