First, sticking with the OP, I have three different answers depending on interpretation.
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As written, with the concerns of cost of some critters, and the advantage of overbroad categories, I’d go with poultry. I’d have chicken as a default, turkey for more flavor, and amazing duck for my ‘upscale’ option.
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If the wizard was ensuring a reasonable cost, but otherwise the broad categories, I’d pick seafood, because I enjoy the huge variety, and the flavor options are immense if I can offset the cost. But that’s not explicit in the OP.
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If the wizard meant to pick a single creature from the poultry or seafood categories to make it equivalent to the single critter options listed first, then it’s pork. Just one avian, or fish, or crustacean wouldn’t cut it for me, and pork is both reasonably priced and quite versatile. Not that beef critters aren’t (beef baken as an example) but at current and likely future prices, I’ll stick to pork.
Okay, if @Nars_Glinley comes back and gives us a clearer understanding of his wizard, I’ll vote then.
Onto @Johnny_Bravo’s well thought out version.
In which case, I’ll be back to my first answer after much hesitation and pick poultry since the cost is mitigated. Swine is now extremely limited by comparison to the other categories. I love shellfish, but eventually I’d get tired of the comparatively limited flavors, even with unlimited non-animal products to flavor it up. Fish are a great love, and has a wide variety of flavors, but not quite enough to compare to the last two.
Bovids would be immensely tempting, and on a different day, -might- beat out poultry. Especially with leg of lamb, roast lamb chops, and the like moving into the affordable (as it’s stupidly pricey in the US) category. But … for the moment, poultry still wins.
With the affordability, I can have delicious ostrich when I want something beefy, duck when I want something fat and savory, chicken for general purpose use. Another advantage is the wizard is being a shit, so if I have to TRAVEL, I’m a lot more likely to find some form of poultry anywhere I go, where larger bovids may not generally be on the menu, or only in forms I may not care for (for example, I’ve had goat, and while not terrible, it doesn’t work for me).
NOTE: If we get a ruling on secondary products (milk and eggs) that’ll also have to come into evaluations.