You can use either one; they're both the same. The second option, however, allows you to change subject if you want: "I always eat a hamburger before my friend watches football." In the past tense, the gerund is still used, the time of the gerund is the same as that of the conjugated verb: "I always used to eat a hamburger before watching football." or "I always used to eat a hamburger before I watched football." Note that the gerund here is a verbal noun. You could use any noun you want: "I always eat a hamburger before football." That last sentence is grammatically correct, but it's not clear whether you watch football or play football.

Both are acceptable.

I think the later one is more suitable.Because when you eat hamburg,you are not watching TV. It's better as follows,I always eat hamburg while watching TV.