I don't see how this question can be answered without resorting to anecdote and stereo-typing.
If anyone's interested in my personal anecdote, I went to an all-girls secondary and loathed it. I was a geek, interested in sci-fi, gaming, coding, graphic novels etc etc. Remember this was back in the 90s when all these interests were pretty niche anyway. I was labelled as being a freak, for having interests that didn't fit in with what the alpha girls deemed "normal". Added to that, I was overweight. I was "Fat Freak" shortened to F-squared for more years than I care to recall. I developed an eating disorder and also self-harmed mildly. The staff preferred the plaster-on-an-amputation approach and brushed everything under the carpet. "Nothing to see here, except our results!" 
All this only ended when I went to a co-ed sixth form, and suddenly realised that I was not a freak, and my interests were not at all niche - they were just interests that had a predominantly male following! I found my group (90% male) and found my self-confidence. If I had gone to a co-ed secondary, I would not have had to endure the bullying I did, because I would have been able to retreat to male friendships.
I now am quite senior in a male-dominated field, and I can categorically say that I am here IN SPITE of my all-girls education, not because of it as generalised upthread (I've noticed that a disproportionate number of "successful" women went to girls schools - balderdash!)
I am equally against all-boys schools, having seen first-hand the misogynistic mindset that the boys develop there over their formative years. All my children go to co-ed schools and are thriving in mixed friendship groups. Life is not co-ed, as succinctly put by a PP.
But, at the end of the day, you must choose the school that's right for your own child. No single person's anecdote can make that decision for you.