Serious Eats - seriouseats.com

I've used all four. Here's my take.
DiningIn charges too much, and takes too long. Nightowl is great for some restaurants, but the great thing is that they're available through Foodler and campsfood for no extra charge. (And since the nightowl website is pretty crappy, I'd rather use Foodler.)

Between Foodler and Campus, it mostly comes down to which site you like better. The only real difference is that with Foodler , you don't have to pretend you live on a nearby campus to find out who delivers to you. They tell you who delivers based on your address. The third time I tried a cfood place and was told by the restaurant "We'd don't deliver to you", I knew I should stick with Foodler.