I've been thinking of enrolling my preschooler to an International school, but I'm wondering if it's really better than just putting him in a normal Manila school?

The first thing to ask is are you really willing to shell out such huge amount of money for your kid's education. If yes, you are one fortunate guy to be able to put your kid to a prestigious school and go do it! In terms of the quality of education, there's no doubt about it if we're talking about international schools. But if you have something else to consider as of now, say, a house or a business, and you'd rather put your kid into a less expensive but quality school, then do the more practical choice. At the end of the day, it's still your call. :)