Hi. I'm so excited to FINALLY be able to offer an opinion, instead of just asking for one!!
We didn't go to Ian Anderson's. His trips sounded great, but they seemed a little "extreme" for our kids. However, if yours are more adventurous, definately send him an e-mail. Vicky at Pook's Hill sent us to Jaguar Paw for cave tubing. It was about an hour hike through the jungle, then a relaxing ride down the river with a stop for swimming.
We stayed at Xanadu on Ambergris Caye. Check out the "Ambergris" drawer, under the topic "Caribe Island vs. Xanadu" for a more detailed report. I also posted a quick report on Pook's Hill. If I can ever get unpacked, I will post a more detailed trip report.