The ing form is normally used in conjunction with some action that takes place simultaneously. An example of this is "I heard him as he was coming in." In a sentence like "I like to have a glass of milk before I go to bed." it denotes a habit, but with an action that comes to an end, each and every time. You'll find some other examples here: http://www.edufind.com/english-grammar/ing-forms/.

Both sound correct.