The biggest difference between the two is the Samsung is Android and the iPhone is iOS. This means a lot of things you can get for free on the Samsung will cost money on the iPhone because of their different app markets. Aside from that the Samsung is bigger and tends to have better battery life. The Samsung will use standard cables for things like charging and hooking it up to a TV or computer while the iPhone will have to have the special cables made by Apple. Functionality wise, they are virtually identical. Both place calls, text, browse the web, etc. One big difference is the Samsung will use Google Maps for navigation and the iPhone will use Apple Maps (which are unreliable right now). Apple has stated that people with iPhones should use the online Google Maps for navigation until they can fix their own Apple Maps.
The short answer to your question is that in most people's opinion, the Samsung is just better.