iPhone 3GS vs. N900 and iPhone 4 vs. N900. This topic has been covered a bit, just search for "iPhone4", sans quotation marks and you will find many other discussions about this very same topic.

Coming to a Maemo forum and asking this; I'm going to assume that you want the N900 to be the winner. And allow me to say this as an iPhone owner, customization in quite a few areas is where the N900 wins.

Words like "better" though, matters on perspective. Read up about the "Simple stuff iPhone should do, but N900 does" to read more commentary that's gone on about this subject too. I'm sure it will help your argument.

Take care.