If you are already into Apple ecosystem and you are fine with 4inch screen then go for iphone 5. However, if you are not into apple eco system and size matters then go for S3.  Its all about what you are looking for. If Map is something you are going to frequently use then Iphone maps sucks with compare to google maps. Specs are not everything but if you do care then take a look at this link.

 http://www.pcmag.com/article2/0,2817,2410034,00.asp