Wallet Can support then just go and get S3 , nice to use and great battery life.
Wallet can't support then just wait for iPhone 5 announced and see that impressed you or not , if not just get the 8GB iPhone 4S by then should be 1600 +- if you still want iOS but it's same little upgrade thinner lighter faster .
I am very eagerly to see what's the new iPhone will offer as well. Reason bought S3 because too boring with iOS for the time being and since there is still around half year till can get my hand on new iPhone , better to try something new first. Well that's me.

Using iPhone for few years continuously and started to feel bored, bought myself a Samsung Galaxy SIII early this month, become a happy man again lol. Mainly because totally new phone and new experience ( again ) since nexus one is my last android. However I really can't stand the typo I keep getting on android , it's not really responsive and intuitive compare to iOS, if you text alot and migrated from iOS , you will know what mean.
Those are still minor glitch and still acceptable. I am also waiting for the iPhone 5 but there is still time so trying out the new SIII first. If iPhone 5 still getting the same old interface without any improvement , I'd keep this SIII and get WP8 instead.
Let's say iPhone 5 launched at December , you still have around 6 months to use the SIII. This phone definitely worth to give it a try.

Build quality I agree with you S3 looks and holds cheaper althought is flagship device from Samsung , but drop resistant phone.. any phone able to withstand drop ?