I voted for Taco Bell. Not because they are necessarily the best (because they probably aren't) but because they are convenient where I live and I go there quite a bit.
I would have voted for Subway, but I have a hard time thinking of any place as fast food that refuses to have a drive-thru. I would definitely go there more often if they did.
Whenever I go out for fast food I am usually in a hurry, so having to get out of my car, go inside, to usually stand in line just so I can then walk along a 30 ft. counter, while telling someone every ingredient I want on my food doesn't really seem like (very) fast food to me.
(excuse the run-on sentence)
...And I agree SC. There tuna sub is really good.