I've not seen this consideration put forward amongst the existing 15 answers to this thread yet, but I think it's worth considering.

From my experience Web Forms is more similar to Win Forms and WPF than MVC is. Given this, I think one might consider choosing Web Forms when the team has most experience in that kind of tech, or when the Web Forms project will deliver an interface on to the same data set as an existing (or concurrently developed) Win Forms or WPF project. Doing so allows developers to cross between projects more easily, since application logic may be quite similar between the two.

As other answers have pointed out, development on the MVC framework is more similar to web development in Ruby, PHP, Python etc than its Microsoft counterparts; so naturally the choice of MVC can be influenced by the teams experience in those areas, along with the factors submitted in other answers.