Joe Swanson is one of the most likeable characters in Quahog. Despite his anger issues and the fact that he left Bonnie when he started walking again (he did return to her, but she tried to shoot him!), Joe is usually one of the nicest people on Peter's street. He routinely sacrifices his body and safety to help other people and is very much still a good cop (as far as that goes in a cartoon) even with the use of his wheelchair. Add Patrick Warburton's voice to the mix and you have a pretty fun character.
When it comes to cameos on Family Guy, you've got two pools to choose from: the voice cameos from famous actors like Drew Barrymore, Hugh Laurie, Patrick Stewart and Dakota Fanning, or the visual cameos where an actor or famous character is simply included without his or her voice. Both can be really funny and it doesn't really matter which one you like the most, but you probably have favorites among both camps.
It really is a wonder why Meg Griffin is so much more of a butt of the collective Family Guy joke than her idiotic brother, Chris. Sure, Meg has joined a cult and done some pretty stupid stuff, but Chris is stupid pretty much ALL OF THE TIME. The boy does get made fun of over the evil monkey in his closet rather than the help that he needs (whether via exterminator or psychiatrist, you be the judge!), but overall he's pretty well-liked by his family and community. His parents also never really do anything about the sinister attention that Hubert gives him, either, come to think of it...
Meg Ryan is not commonly cited as a favorite character among the cast of Family Guy. She's considered the lamest member of the family despite the fact that her brother Chris is a flaming idiot, the dorkiest guy in school lusts after her and she is detested by most people. This is especially weird since she looks just like her mother, who is considered one of the coolest people in Quahog. Meg is kind of like the "red-headed stepchild" of the family and bears the majority of insults from all members. Even when people are nice to her it's usually the butt of a joke.