Favorite Co-op Class?

I want to teach a class at my daughter's co-op in the spring. Actually, 2 classes - possibly even 3. I've been struggling with the decision of 'what' to teach to 4th-6th graders. So, far I've thought of:

• Nuts About Nature based on Melissa's co-op study
• Think! based on the Think! website
• Nim's Island based on Liberty Hill House's posts (I'd need another literature study for 2nd 8 weeks)
• Jungle Book study based on Little Blue School's posts
• Getting to Know...Famous People study based on Mike Venezia's books - we'd read a different book each week and I'd come up with activities to do - sounds like fun, but the most work
• European Vacation where we'd take a few weeks to a month per country and explore various European countries - I love what Fireside did with Italy and Renaissance Mama did with France recently
• Where in the World is Mrs. Waffenschmidt? class - perhaps mapping and creating notebooking pages as some of you recommended when Alex & I started this before
• Journey North class based on Journey North's Mystery Class

So, I'm really torn and having a hard time figuring out what I should do. I want it to be lots of fun. I also know that the 2 things I think Alex needs more of are science and geography, so this should play into my decision. I like the idea of creating my own study, but this is also more work.

Do you belong to a wonderful co-op? Do you have a favorite co-op class? I'm just really struggling with this and would love some input. Thanks!