Wow, that's a toughie. "Celebrity" suggests that we're talking about a famous person's public persona, rather than his or her body of work, and I don't often think in those terms. I mean, there are a lot of people whose celebrity seems... self-referential. They're famous because they're famous. Back in the Seventies, they'd be the panelists on game shows.
So, back on track -- I'd say my vote Favorite Celebrity is tied between Katherine Hepburn and Paul Newman. Lady Kate is simply the Goddess Of Pure Class, in her public persona as well as her on-screen roles. Meanwhile, Paul Newman has pulled off the neat trick of exploiting his public persona for good causes, setting up his Newman's Own brand to give all its after-tax profits to charity. Class acts, both of them.
2. Who is your least favorite?
Well, let's see... I'm gonna file my dislikes for the Mouthpieces of the Religious Reich under "Body Of Work", and give my vote for Least Favorite Celebrity to the eldritch horror that is Michael Jackson.
3. Have you ever met or seen any celebrities in real life?
Okay, again, I'll leave out famous actors that I've seen on stage and moderately-well-known people like writers and artists who don't really have "Celebrity Status".
I've met Stan Lee, the master of self-promotion.
I've seen DeForest Kelly, Gene Roddenberry, and The Captain and Tennille (hey, they were celebrities back then).
4. Would you want to be famous? Why or why not?
It might be interesting. I wouldn't mind using fame as a lever to get people to listen to the Causes I Find Important.
5. If you had to trade places with a celebrity for a day, who would you choose and why?
George Will, Rush Limbaugh or some other conservative commentator, so I could savage those who richly deserve it from a pulpit that will get attention from those who most need to hear it.