Oh you're not alone - I'm almost in total meltdown.
I'm afraid we've only managed one school visit so far. As ds is the youngest of three, we've been round all the schools in the area twice in recent years and he was involved in most of these visits. I don't really feel you learn a lot at open days/evenings anyway - they all try to put on a good show. I remember with DS1 we visited our nearest non-selective (subsequently put into special measures). DH looked at the nice new building, listened to the HT's speech, then turned to me and said, "oh this is nice - this'll do won't it....?"
I've tended not to involve him much in school selection since then.
What I did with ds1 and ds2 was draw up a table setting out the criteria that we wanted to take into account and gave each school a score. We included things like size of school, ease of journey, whether or not they were allowed mobile phones (didn't want my kids travelling on public transport without one), what they were like for sport and science, mixed/single sex, what grade Ofsted gave them etc etc. Not a very exact science, but helps to focus your thoughts a bit - you can always manipulate the figures if you don't get the result you want! Don't underestimate the importance of a good journey. When they're lugging sports bags/musical instruments/heavy school bags to school they don't want to be changing buses/walking too far and you don't want to turn into a taxi service!
It's really difficult to make a choice on the basis of one visit. I remember going to one open evening a couple of years ago when it was dark, pouring down and I had a really bad cold. I hated the school - thought it was tatty and run down and wanted to leave almost as soon as I got there. Went back the following summer to watch a cricket match ds was playing in and thought how lovely it was!
At least this time next week things will be a little clearer!