Which iphone model is most popular?

Like which model do more ppl have?( 4, 4s, or 5)?

It depends on the the time of the year, newer iPhone's only sell really high during the holidays seasons in the fall when they get discounts.
http://www.tech-thoughts.net/2013/05/global-smartphone-market-share-trends-android-iphone-windows-phone.html#.UdDdE_mR-So
Here is the chart by market share, the iPhone is in grey and you can see a spike every year in Q4.
the rest of the year the iPhone 4 and 4s should be doing just as good as the iPhone 5.
With that said, if you are looking to buy a new smartphone, you're decision shouldn't be based on popularity but which one fits your needs, the iPhone 4S for example does basically the exact same things as the iPhone 5 just a second slower when it comes to loading web pages.