We've also been struggling with the public/private issue.
Due to a house move, we've been finding it difficult to find a decent school place for dd as they're all full (the London bulge stuff that's going on) so were looking private as well.
In the end, we decided against private for now.
Partly because we felt it too much a financial commitment at the moment because dh's work isn't secure, even though we could scrape by.
Partly because of dd's character. While we liked a lot of aspects of the private schools we saw, some of them were way too disciplinarian which dd would not react well too (one of them had kids sitting at desks facing front in reception, another had even the nursery kids wearing full uniform with a tie and standing up when an adult walked which I thought was just ridiculous - they're 3 years old!!).
I do prefer the smaller class sizes but after a year at state school with 30 kids in a class realised that dd is thriving - she's a confident, quite outspoken and very independent child. I'd probably be less inclined to state schools if my child was quieter or more withdrawn.
After weighing it all up, we decided to give the state options a go and consider independent for secondary (when dh will hopefully be more secure or we'll have more savings), depending on what the state options are at that point. We'll also have the money available for extra curricular activities or tutoring if we feel she needs to be stretched a bit more - still far far less than going private.
So, like other posters said, it so much depends on your child and the options available to you. That said, if money were no object, then I think i'd plump for a couple of the private schools I saw - but for us as a family right now, it would be too much of a sacrifice given that I think dd will do very well in the state as well.