The Samsung Galaxy S3 is already considered old. When
thinking about a new phone, the Nexus 5 comes to mind. This video reviews the
two devices, focusing on design, physical format and screen. Also, Vellamo
Benchmarks are run to compare their performance on different tasks --- all trying
to figure out if the upgrade is worth or not.
My conclusion is that there's no doubt the Nexus 5 is better -- in particular in terms or processing and display quality. That makes an upgrade really worth if you do a lot of gaming, heavy apps or reading. For internet browsing however, the difference is almost non-existent -- in which case keeping the Samsung Galaxy S3 for some more time would not be a bad idea.