Protagonists should always be the most dynamic and interesting character in the show, or else it would make no sense to center the show around them.
Take Eddy for instance. Although Ed and Edd serve as the brawn and brains, Eddy is the one that comes up with schemes and plans that thrust the plot into action. It wouldn't make sense to have the Big Picture Show not center on him (Are you reading, Adam Muto?).
The character can win or fail or do neither, as long as the journey is funny and interesting. It's funny by use of jokes and silly animation. It's interesting because the plot twists and bends and you aren't certain the protagonist will win or fail. Characters aren't sympathetic if they usually win, but always losing is also frustrating and removes the mystery of if the protagonist will succeed.
Another example is Invader Zim. Both the eponymous alien and the big-headed boy are both protagonists and antagonists to each other. This is interesting because both win and lose on a regular basis. Zim claims victory but it's very minor and he is no closer to conquering Earth, Dib loses but he still has a place to call home. The insignificance of their victories and losses lend well to the idea that this interplanetary battle is happening on the scale of fighting skoolchildren. What is important is that the two are dynamic, interesting and funny to watch. I don't know how the new TV movie is going to fuck up (aside from awful redesigns) but that's an essay for another day.
Characters shouldn't be all-powerful or else the conflict gets boring. This is the biggest problem with Rick's characterization in the later seasons. Rick went from being a crazy grandpa that lives life on the edge to a cynical god that seems a little too uncaring to make us believe in the conflict and danger each plot provides. Rick could be the smartest man in the universe, but just from what he's aware of, so he's always on edge.
My personal ideal is a character that is undeterred from failure and is constantly put in new situations to see how he would react, instead of just the same failure over and over again. Someone like Lord Hater. He is seen as the antagonist but has his own stories, his own pet, his own love interest and even his own awesome climax in the last episode. Most importantly, he's funny to watch!