How do I select the right iPhone carrier I have seen a lot of people asking about what carrier to use and what features they have. 

Also people have asked about Visual Voicemail, which confusingly is not available on some networks, although Apple highlight it as one of the iPhone features, without mentioning it is not available to all carriers. Source

Also I have had many people ask about using a Personal Hotspot or unlocking the iPhone.

Where can all this information be found?
I asked this question so I could answer it, as I said there are a lot of people asking me about this issue.

On this page of Apple's support website, you can find a list of worldwide carriers and the features they support on the iPhone.