Uncle Junior has to be up there. In the first season, he was trying to be boss and had some kind of a status/social life. He even had a steady girlfriend. He got tricked by Tony into thinking he was the boss, got manipulated by Livia into killing Tony, and ended up getting caught up by the Feds because they thought he was the man.
By season two, he's on house arrest and he's under constant surveillance by the Feds. His crew was decimated and he had to do Tony's bidding. His only lifeline was Richie, somebody that wasn't respected and couldn't sell the idea of killing Tony to the guys that mattered (Albert Barese). He had to lie to Tony that he was playing Richie the whole time just so he could prove his usefulness to him and get more money.
He ends up with cancer, the trial takes away most of his money, and he has to fake dementia to end up getting off. He gets hit with a boom mic and gradually develops dementia for real. His only purpose by season five is to be Tony's other consigliere, which he was great at. He literally goes to funerals for people he barely knows just so he can leave the house. Calling somebody's wake an after-party.
He lived his whole life with dignity. By season six, he's a fukking drooling idiot, a scumbari. He ends his relationship with Tony forever by shooting him, thinking he was p*ssy Malanga. Even Bobby, his right-hand man and caretaker, is uncomfortable being around him after that. The only thing you can say about Junior is his dementia kept him from dying with the memories of being in the mob. Unlike Tony, he can just say "that's nice" and live the rest of his life knowing that if he dies, people can't even wear his shoes.
Junior's ego might have killed him faster than anything else did. Imagine if he had no interest in being boss. Imagine if he didn't break up with his girlfriend because everyone found out he's a bushman of the Kalahari. Imagine if he didn't try to get Tony killed. He could go down to Boca whenever he wanted. His crew would still be intact. He would be one of the most useful members of the family. Instead, he lost everything chasing a title he wasn't built for.
