There are many different kinds of tuna. Albacore tuna, which differs greatly from ahi tuna in color, is the tuna used for tinned tuna (95% of all albacore harvested is canned). Also, to quote Wild Pacific Seafood, "there are significant differences in methods of catching, sustainability, and the product itself."
Of all the tunas, albacore is the lightest, it has the highest level of omega-3s, and it is among the mildest. Because of its light color, albacore is often called the other white meat. The phrase "chicken of the sea" was meant to call light fleshed meat to mind. (Sorry Charlie!)
Albacore has a steak-like texture that makes it great for grilling and searing. It is listed by Seafood Watch as a "Best Choice" and is MSC Certified. Moderate mercury. Kosher.
1 lb. for $16.50
-- Seared Tuna with a Ginger-Garlic Marinade (Cooks Illustrated)
-- Grilled Tuna Salad Niçoise (Gourmet magazine / Epicurious)