I had a choice between the S4 or an iPhone 5. I chose the iPhone 5 and I don't regret it. I previously had an S3 and it was slow. It turned off randomly when I needed it most. Your best bet is an iPhone 5, not 5s or 5c because there is absolutely no difference.
The S4 is extremely slow in my opinion, I had a test run for about 3 days and I only downloaded 3 applications & it was slow as hell. I recommend an iPhone 5, you won't regret it.
I am using the s4 right now. Best phone I have ever had. Never had any problems with it. Way faster than my previous iPhone 5. Not to mention way better features.
You get more freedom with a galaxy then a iPhone. It's personal preference though.