I use some HTTP Handlers from my Web Forms days forms, to for example Generate Images Thumbnails, Serving CSS, Etc…
I like them, they are easy to make and offer great abstraction. Can I still use them with optimal performance in MVC or should I use Action Filters?
Action Filters add several more layers of abstraction, because they go thru routing and MVC handler. If you are THAT concerned about performance and don’t need any MVC features, you should stick to Handlers.