We had the same problem a couple of years ago and having looked at the privates (all bar one!), our local state was outstanding and we felt that if she was going to do well anywhere it would be there. It was also in the same village, so would make local friends and we would revisit the decision at Year 3. This was also partly because we weren't so keen on the preprep part of one school and disliked the 'snobby' head in the other!
Last September, at the start of Year 2, we moved her from the state to private (the one that we hadn't visited until then).
I won't go into the reasons for moving her, but it was such a huge decision for us, that went fairly smoothly for her, however, there is definately a difference in the standard she was at (although this will depend on the school), so she is still catching up a little, mainly in maths and writing, but it is getting there.
I frequently ask myself, what would she have been like if she had been there from Reception!
However, the advantage of being in the state school for the first two years, is that she has made some lovely friends in the village - who we still see and meet at Brownies and of course saved ourselves the sum of around £18,000 in fees - which when you look at it that way, is a huge amount.
Go visit the schools, see what the differences are, speak to other parents. It is so difficult, because you don't know how your child will be at school, some children will do well wherever they are, some seem to need that little extra input and benefit from smaller classes, unfortunately you won't know what type your child will be until they start!
Just be aware that writing a cheque out for £2,000 at the start of each term, does hurt a bit and it really hits you the first time you do it, of what a commitment it is!
OH (privately educated), has major regrets we didn't send her sooner, me (state educated), not so much, because of the friends she made, but I still can't stop thinking 'What if' we had, especially when I see her working so hard.
I think for us, school choice was the hardest decision we have had to make for our dd so far!!!