What can you do with chicken that you can't do with fish?
General Tso's Fish?
You can sit around and watch the game with a big platter of buffalo wings. When was the last time you saw someone eating buffalo fins?
The list goes on. I like fish as much as the next guy, but chicken is much more versatile, so that would have to be my pick. Although of all seafood, I don't think crab is given nearly enough credit. Good crabmeat is, in my opinion, even better than lobster or steak.
Chicken is bland and to reach any sort of level needs to be paired with a sauce or filling. But when you look at a piece of fish, before you say I can serve it with so and so sauce, you can marinate it, you can serve it sliced thin and raw (you could do both of the first two for a ceviche), you can cook it to wide variation of temperatures, you can cold smoke it or hot smoke it, you can barbeque it, etc. Some of those cooking styles come into play with chicken, but some don't, and that's before you get into specific seasoning. I can take a piece of sole, stuff it with king crab and shrimp and camembert. You think cordon bleu is good, that'll knock your socks off. Tilapia with a parmigiano crust doesn't need to be drenched in marinara. You can use soul or flounder for francese, which is a classic preparation. Chicken has a limited scope in that regard, as your going to need somethinng to mask it to get it the extra mile, whereas not just the variety in fish, but the fact that it loans itself to many different ways of cooking itself, make it a more valuable agreement. I'm not going to throw thirty herbs on my fried fish because I want to taste the salmon or cod. Whereas you taste chicken, which doesn't have much depth of flavor on its own, and you know what you're getting in terms of the meat no matter what the preparation. The sauce will be different, but the meat itself will not change too much. But you take some pieces of raw salmon. Cure one like gravlax. Cold smoke one like smoked salmon. Fry one on it's own. Bake another. Deep fry another. I'm not talking about seasoning it outside of salt and pepper, but in terms of testures and tastes, your going to get more out, and that's just salmon. Throw in the otoro of the tuna. Cured anchovies, which make wonderful bases for other sauces and dressings. Dried shrimp, if we head that direction, are the basis of many great Filipino dishes. Southeast asian cuisine cannot exist without fish sauce. Fried calamari. Shellfish boils. Grilled unagi. Chowder.