IPHONE 3GS has better User Interface and a lot more apps and it has a Capacitive screen on the other hand Satio has 12MP Camera,and more screen resolution and has Symbian OS with Resistive touch screen which requires more pressure than Capacitive screens to register a command.
Here is a good link for side by side comparison in terms of specs:
http/www.gsmarena.com/compare.php3?idPhone2=2683&idPhone1=2826
What are your needs from a mobile phone ?