Generally speaking, it's rude to pick one member of a family and call them your favorite. But since the Addams family aren't afraid of being rude - or at least, they are unaware of what constitutes rude behavior - it seems kind of fitting to pit them in a death match against each other and to crown one of them as "the best Addams."
Let's meet the contenders: The parents of the tribe are Gomez and Morticia, and they are so macabre that when a nanny suggests that they send their kids to an outdoor summer camp they wince like they'd been shot. Then there's Uncle Fester, a bald weirdo with bug eyes and a wide mouth who can light up a lightbulb just by putting it into his mouth. Young Pugsley collects serial killer trading cards and helps his sister put Pubert, the baby of the family, into a guillotine that's been tucked into the attic. These are all strong contenders for the throne. (Well, minus Pugsley, whose whole character is basically "a chubby mostly silent sidekick for his sister.")
But as kooky and spooky as those characters are, the best of the Addams clan by far is young Wednesday. Now, to be fair, it's a bit of a rigged game, because the movie's script is tilted in her favor, giving her the most chances to be funny. (When she's stuck at the loathsomely cheery summer camp, she starts organizing a rebellion against the Wasp-y camp counselors, while her parents are sidelined back at Addams manor. Gomez never stood a chance in this tournament because he doesn't have a plot to call his own.) Even so, Wednesday is the fullest expression of the family's wicked sense of humor, because their morbid worldview is the funniest when it's coming out of the mouth of a child.
It also helps that Christina Ricci is so unbelievably good in the role. There is a scene where the counselors, tired of dealing with the belligerent Addams children, lock them into a shed with a VCR and tell them that they can't come out until they've watched every movie in their family friendly collection. We cut to the exterior of the cabin and watch as day turns into night, and as the sound of Sound of Music fades into the sound of the Brady Bunch. When they are finally let out, the counselors ask to see Wednesday's smile. She gamely tries to turn her usual grimace into a happier shape by slowly pushing one corner pf her mouth up and then slowly dragging the other corner up till they match. The problem is that her eyes still look deranged, and the total effect of her crazy eyes and fake smile is even worse than her grimace. It's the biggest laugh in the movie, and it's totally due to young Ricci's ability, because that joke would not work with a less talented actress.
Sure, all of the actors are great in their roles. Raul Julia brings a lot of suave charm to Gomez, Anjelica Huston embodies Morticia with deadpan panache, and Lurch just has to stand there, looking tall and creepy, but boy does he look tall and creepy. But of all of them, Ricci walks the thinnest line and succeeds the most. Her character is actively hostile - as I already mentioned, she attempts to guillotine of her newborn brother - but she manages to keep Wednesday funny, instead of making her look cruel. That distinction is important for keeping the tricky tone of the movie in balance, because these characters have to be obsessed with evil while not being evil themselves.
For all of those reasons and so many more I'm rooting for Wednesday to win this hypothetical free-for-all. Hell, for all I know she's already won the damn thing - it's been twenty years since we've seen the Addams on the big screen and we all know she has access to murder weapons.