I get asked this quite frequently.
It depends on what you want for your child. Many parents want an education similar to what they had, even if they acknowledge that it had limited utility in their own life (Loader 2007). If this is the case then you can't make a rational judgement. If you can work out what skills, knowledge, environment will suite your child then this is a good starting point.
Conventional wisdom says - go to the school and look around, talk to parents who have kids at the school. This is good advice. Just looking at published academic results really tells you very little about the school for many reasons.
What is a good school? A lot of research in the western world suggests that in the eye-of-the-student their are very few 'good schools' - if on-balance, most students would rather avoid school than attend then schools are not making the grade on a massive scale. Other research shows that high performing students will perform comparably no matter where they are (Freakonomics), and that there is more variation in student learning between classes than their is between schools. So don't make a decision on academic grounds only.
A common misconception is that your child is smarter than they actually are. Most kids are average (by definition), but most parents and students see themselves as a bit above average. This is a hard pill to swallow- but guess what the world is full of average people doing all srts of amazing things because they put their mind to it. Its not so much the metal horsepower that matters for most jobs, but the amount of effort put in over a long period of time. Being driven to learn and improve for the joy of learning is enough.
In my own opinion - school trying to personalise education, or change towards knowledge era schooling or genuinely undertaking a Montessori style approach (in lower grades) are on the right track.
Go for a school that is committed to making education exciting and relevant for the kids, uses a variety of modern technologies in the classroom (not just electronic white boards), and is focussing on students becoming better learners.