I vote for creepy on New Town too.
I think it's fair to say that often opinions on schools are just that, and I always suggest checking out real test scores (the links Shadowcaver gave are great ones) but if you're curious as to the general feelings amongst those who live there and each schools reputation, I can happily provide that.
Orchard Farm is really small, they have a lot of poorer kids (though looks like this might be changing as areas in the district grow up (like New Town) This would worry me as they'll be going through some major growing pains soon.
St. Charles has a lot of older buildings, esp. the elementary schools. However, the high schools are more recently updated. They have struggled with test scores relative to other school districts in the area, most people think that's because of the broad socioeconomics of the kids attending. They don't have the strong tax base of Fort Zumwalt (which has Mid Rivers Mall) so they don't have the newest text books and technology, but they offer a wide variety of programs.
My mom is a special ed teacher at St. Charles High and has been pretty happy there.
They're not growing very quickly anymore, which is a good thing.
Francis Howell was growing at a rapid pace through most of the 90s as the outer areas of St. Charles and much of St. Peters grew crazy fast. Then they kept building new schools and moving boundaries, so when I attended I was switched around a lot. Most of their schools are 10-20 years old now, and everything is pretty up to date.
Their gifted ed. program used to be (and may well still be) one of the best in the state.
Again they don't have the best of retail tax bases.
Fort Zumwalt is newer and is growing by leaps and bounds right now. They're doing the building that Francis Howell was 10-15 years ago, so their facilities are new but they've had some growing pains. Expect to vote on a bond issue just about every year. Parts of this district are a little more rural (though much less than 10 years ago) so I know they had more problems with meth use and teen pregnancy than Francis Howell did. That's not to say they were serious problems or that they haven't been taken care of now, but that was the reputation in the early '00s.
Hope that helps, if you have any questions feel free to ask.
As I said, this is all anecdotal and based on the general opinions of those who live in the area.