I looked in to this for daughter's phone and for mine.
As someone pointed out, it depends on what you want the phone for, and how rich you are feeling.
Daughter got the Galaxy S - it is so much more flexible than the Apple, and in the UK it is cheaper,too.
You can have spare batteries. You can increase the memory.
As someone else has said, the Android apps tend to be lower cost. There are now plenty of free ones to download.
Negatives about the Samsung experience .
1. The Kies soft ware can be very fussy. I do not log in to our pcs as an admin., but the Kies software only works when you log in as admin. If you play around with the Samsung too much, the software might not recognise it.
2. There are a number of ways of connecting with pcs. I connected once as a mass storage device to download lots of music to a micro storage thingy in the phone.. To connect to Kies now, I have to take out the full micro storage thingy and put in an empty one. Daft.
The software is supposed to update via Kies. Mine won't. Dunno why. I do not know what I am missing. I do know that the BBC iplayer will not work on my older software. Shame.
3. There are no helpful "Samsung" stores. If you take a broken Apple to an Apple store, at least you get a (nearly) human being to talk to.
Despite all this negative stuff, I bought a Samsung Apollo for me. Works fine. It is the cheapskate's version of the Galaxy S.