Depends on the language, but when you have to use some metaprogramming gymnastics, then types are really hindering to develop something generically, if the language doesn't provide a fully developed type systems, which few systems have. For example higher-kinded types are quite essential, but not always given. Then I prefer dynamic typing and get this done fast without safety. But then I remember getting a lot of bugs in certain types of applications, maybe one fifth, or something.