The thing that bugs me about tuna is that each can contains 32-33 grams of protein, yet a can of tuna isn't very filling. If you're trying to eat 200 grams of protein a day, that means you can only have 6 cans, which really wouldn't fill you up and you'd have too eat a lot of carbs.
On the other hand, it takes about 6oz of chicken breast to get the same amount of protein which is a lot more filling.
Too much protein will make you fat just like anything else, so chicken seems like a better way to go, even though it is more of a hassle and has some saturated fat in it.
If you are trying to get 300-400 grams of protein per day though, tuna and whey is probably the best, IMHO.