>>76639968 (OP)
I eat both at least once per week. Between the two, I would strongly advocate for sardines. I love them. They are a perfect snack, and contain high protein and micros. They also have much fewer heavy metals than tuna, but be cautious. If you are eating bullshit-brand whey protein (or even worse, beef protein powder,) and also enjoy deenz recreationally, then you might be overdoing it on arsenic. There is about as much arsenic per serving of whey as there is in a can of deenz, and that is not counting whatever else you eat in a week. Make sure your shit is good, and manage your diet accordingly.
I am also a big fan of canned cod, mussels, mackerel, kippers, and other fish.