Why just these two? Are you trying to compare the worst of the fast food burger joints or intentionally leaving out everything else thinking they would look better?
Burger King is just gross, I prefer McDonalds but even then, I don't get their burgers, just chicken selects, shakes, fries and McFlurries.
Unfortunately, the shakes, fries and ice cream are better obtained elsewhere.
If I want a fast food burger I go to Dairy Queen and say ketchup only so they make it on the spot and it's burn your tongue hot.
However Arby's is genuinely "the spud" and cannot be beaten. The sauce.. the roast beef.. the fake cheese sauce............... there is truly no competition.
Subway is good but there's places I'd rather go. Jack In The Box is better than McDonalds and Burger King though.
If I want to go out and buy burgers though I'd just go to In-N-Out if I was in California or BurgerMaster here (local chain) which are good. Except In-N-Out's fries, those could stand improvement.
Really though, gross luke-warm food vs greasy fatty food. =\ =\