Pig is an awesome species, probably one of my favorites. I have a number of Pig villagers that I'm fond of, including Agnes, Boris, Chops, Cobb, Pancetti, and Rasher. Heck, I don't like them as much, but I'll throw in Curly, Gala and Kevin here too, they're good.
It's tough to pick one favorite.
I'm inclined to say Cobb because his mad scientist-themed house in New Leaf, combined with his green skin and yellow eyes, gave me the personal headcanon that he was in fact a mad scientist who was affected by his experiments. However, his house's interior design took a real hit in New Horizons since the mad scientist set isn't in the game. That doesn't really matter to me personally since I have him as a resident in New Leaf but not in New Horizons, but I'm looking at things overall, so it is still a negative.
Chops has a definite case because of his Smug personality (my favorite male villager personality), his great character design with his hairdo and moustache, his great fashion sense in New Leaf with the Red Ringmaster's Coat, and the pleasant, fancy interior design of his house in both New Leaf and New Horizons.
I like Boris for my own sort of headcanon reasons. His name, Boris, makes me think of the actor Boris Karloff who was famous for portraying Frankenstein's Monster in Universal Studios' 1931 film Frankenstein, along with its sequels Bride of Frankenstein and Son of Frankenstein. This ties into his New Leaf house featuring a bunch of movie-themed furniture, like the Lobby Floor, Floor Light, Popcorn, Speakers, Standing TV, and Theater Seats. An English gentleman, Boris Karloff was also known to drink tea during breaks while filming and there of photographs of him doing so while in the Frankenstein makeup, and you're able to acquire a Cup of Tea from Boris' RV in New Leaf as well. While Boris' house lost all of that in New Horizons, I can't really complain because his house is now Ancient Egyptian themed, and Boris Karloff played the mummy Imhotep in Universal Studios' 1932 film The Mummy. Either I'm onto something or this is a wild coincidence, but I love it either way. I'm also fond of his unique tusks and his Cranky personality, since Cranky is my second favorite of the male personalities.
Rasher is simply loveable. He has the great Cranky personality, and his character design is awesome. I like the scars on his head, and his really distinct smirk. His houses' interior designs aren't all that good in any of the games, though at least the exterior looks neat in New Horizons judging from the picture on the wiki.
Agnes and Pancetti are two of my favorite Pigs as well, like I mentioned above, but while I like them a lot, I don't have a lot to say in this regard. The boys just have a lot more going for them.
As much as I like them, since Cobb and Rahser's houses are real stinkers in New Horizons, I'll let it come down to Boris and Chops. I love Chops, but I think I'm going to give it to Boris. There's just too much there coming together, intentional or not, that just appeals to me personally. Also, because of all of that Boris Karloff and Universal Studios stuff I mentioned, I also like to headcanon that his tusks are vampire fangs to tie-in with another Universal Monster, Dracula, who was famously portrayed by Bela Lugosi. That bit's just something I like to attribute to Boris that isn't really a thing just because I love the classic, old Universal Monster movies, and he and Cobb are both residents of my main, horror-themed New Leaf town so I wanted to give him a little extra.
Also, it's a shame that Pigleg was dropped over the course of the series and didn't make a return in New Horizons. He would've fit in well in this game since it's set on an island, and I would totally have had him as a resident.