Tuna is delicious, but i must admit, that salmon is the most delicious fish for sushi in my opinion and its taste is multiplied by the shushi vinigar and (rice wine) in the rice and/or by the liquid of the pickled ginger and also expanded by avocado, Nori, cream cheese.
I love nearly all sushi with fish, but man the sake (salmon) ones i could die for. It's the umami (protein-ly taste) taste of the raw salmon, that just makes my taste receptors explode and makes me happy.