The biggest downside to the iPhone is Steve Jobs. However, Steve Jobs is the biggest upside to the iPhone.

To be honest, I've bought an iPhone 4 for the missus and I have an N900. Each to their own, she has no use for the functions I can perform on my N900. Equally, I couldn't be tied to an iPhone and its restrictive nature (without jailbreaking).

You don't tend to find 'honest' and 'unbiased' opinions, certainly not on a forum such as this. Read everything you can about both on the internet and draw up 2 big lists. Strike off any similar functions and it'll leave you with the differences. Choose the most differences that suit you, there is the reason that phone is better...for you.