I currently have the iPhone 5. I'm thinking about switching to Android. Should I get the S4 or wait for the S5? Don't know yet :P
Wait for the S5, it should be getting released around March.
Sources: http://www.ibtimes.com/samsung-galaxy-s5-release-date-coming-mid-march-retail-launch-tipped-samsung-exec-may-sport-cheaper (http://www.ibtimes.com/samsung-galaxy-s5-release-date-coming-mid-march-retail-launch-tipped-samsung-exec-may-sport-cheaper) / http://www.ibtimes.co.in/articles/539779/20140220/samsung-galaxy-s5-release-date-10-expected.htm (http://www.ibtimes.co.in/articles/539779/20140220/samsung-galaxy-s5-release-date-10-expected.htm)
Honestly if I were you I would go with neither. My friend owns the previous geeksphone, which runs off of firefox os (which is super fast, only problem is the lack of apps compatable) and has super loud speakers. They are coming out with a new one, which has the choice between Android and other os's. But the main reason this is better is because this has an intel processor, which is the first time one has been put in a phone. This is, to what I have seen, the best phone that's out at the moment. http://shop.geeksphone.com/en/phones/9-revolution.html (http://shop.geeksphone.com/en/phones/9-revolution.html)
So today there was an unveiling event of the Samsung S5. So here's a comparison of both the S4 and S5: Samsung Galaxy S5 vs Galaxy S4 - Quick Look! (http://www.youtube.com/watch?v=71AwicZx19w#ws)
Me and Nebulas Galaxy Note swagger.