MessageHandlers vs Filters in asp.net mvc web api project

What's the difference between using a MessageHandler vs a Filter to check for an API key in the request header for an MVC web api project. I see that there is a well outlined example of a MessageHandler for just that purpose in http://www.asp.net/web-api/overview/working-with-http/http-message-handlers e.g. ``` GlobalConfiguration.Configuration.MessageHandlers.Add(new ApiKeyHandler()); ``` But it looks like I can do the same thing using a filter as well. ``` GlobalConfiguration.Configuration.Filters.Add(new ApiKeyFilter()); ``` Assuming ApiKeyFilter and ApiKeyHandler both just look at the request header and check for an api key, Which way is more efficient? What's the difference?